The least expensive ones that I know of are Cooktek's MC1800 "Heritage" (20 power settings with a 27 step alternate "temp" scale) and MC1800G "Apogee" (100 power settings). Been a few years since I used one, but I recall that the timer could
could be set for up to 11 h. 59 m. and otherwise did not kick in until
intentionally engaged. These are full-on commercial/industrial products --- officially, the warranty is no good for home use. Built like tanks and priced accordingly. IIRC correctly, katom.com currently has the lowest prices for these: around $700 for the Heritage and $850 - $900 for the Apogee.

But, why not invest in a good (if not excellent) spring-valve pressure cooker such as a Fagor or Kuhn Rikon? They will do the job of extracting flavor, gelatin and minerals much faster and often with better flavor than a two day simmer. Also, because the pressure keeps the broth from bubbling much, it results in a relatively clearer, cleaner broth, as well.

Thanks. Those are a bit out of the price range I am hoping to find, I could see myself maybe going up to maybe $500 for the right unit.

Your point about a pressure cooker is probably a good one although I have never tried it. However I like the ritual of the slow simmer and the way it makes my house smell wonderful for days.

I have a Caso - I know that I ran it overnight but not sure how long it will run. Ours is 4 years old. I used it hard for over a year including during our reno. It could run on various settings or I could set a temp to hold. It has a slow cook mode as well.

This is the same one that I have and still available! It lists a timer but not sure you have to use the timer - unless it is a new addition. If you live near me (SE Michigan), you can give ours a test run.

Caso induction cooktop - Amazon

Cookteks are "a bit out of the price range I was hoping to find?" No kidding. That is why I have wanted but never bought one. Never noticed the Caso C21 before. Clearly, it has auto-shut-off for pan overheating (as when a pan boils dry) and does have (only) a engaged 120 minute timer, but not clear if it also just shuts itself off after two or three hours of unattended usage, another supposed safety feature. If interested in it, you might call Williams Sonoma which also carries this unit.

I did remember something else to consider for that long simmered (non-PC) bone broth production --- if you can wait until next winter to get it, that is.

The upcoming "Paragon" induction unit from the GE spinoff company, FirstBuild. The Paragon, which is supposed to be released "sometime" late this year (December?) will have a comparatively more budget-friendly $249 price. The big deal will be the Bluetooth temperature probe/controller that hangs in your pot to communicate with the induction base for +/- 1°F temperature accuracy. Also programmable/controllable via smartphone apps. Supposedly works for everything from very long, low-temp sous vide cooking to very hot precision deep frying. (Near as I could tell, the time limitation is with the batteries in the Bluetooth probe.) There was an oversubscribed kickstarter campaign, some CNET buzz, and several blog type discussions from the FirstBuild folks this spring. If you want to Google the info, try "FirstBuild + Paragon + Bluetooth" for a search string. I don't know what happens to FirstBuild now that GE is selling its appliance divisions to Electrolux.

Thanks a2gemini, I will check that model out. And thank you for the offer to check it out in person, I used to live near SE Michigan in Genesee and Livingston counties, but I am in Raleigh North Carolina nowadays.

@JWVideo, that Paragon device is interesting, I checked out their old indiegogo campaign video. Looks pretty neat. I wish they designed it so that the probe plugged into the base for power instead of running on batteries though, seems much more practical. However it is a great idea to combine a temperature probe with the induction burner like they did.

mkeys - Hope you enjoy your test. Wow - I looked up the Cooktek and am still catching my jaw - they are quite expensive but some can be built in.

Interesting Paragon device - I rigged up my All Clad probe on my Wolf when I was cooking a big batch of beef stew. It gave me the confidence to know that I could slow cook on my Wolfie. Maybe I could have made a fortune by marketing my idea!

I love my fagor pressure cooker. These new pressure cookers have multiple release valves and it would probably take effort to make one explode. Mine has only worked extremely well. They are not very costly and they are really helpful.

I agree about Fagors. Cook's Illustrated/ATK recommends Fagors and those are what they use in the test kitchens. I have and frequently use both a 6 quart Kuhn-Rikon and a 10 quart Fagor. I find the KR is easier to use but, when I needed a bigger PC (for when making larger quantities of stocks and broths, among other things), the Fagor Duo was 1/3 the cost of the comparably large KR. FWIW, one can buy a 10 quart Fagor "Rapida" model from Costco/Costco.com for $100 and they also sell a combo-kit with both a 4 quart and an 8 quart PC for less than that. Some folks find a that 8-quart capacity PC is sufficient for their broth and stock-making.

I was taught to make stocks and broths the way mkeys does it --- which was a long time back in the previous century --- but I find the PCs are so much faster and better. The big deal with making stocks and broths in spring valve PCs like the Fagors and KRs (as opposed to the old style jiggle top/weighted-valve style of PC or the long stockpot simmer) is that the spring-valve models vent very little steam thereby leaving better and more concentrated flavors in the stock or broth. For a somewhat scientific testing of how much better spring-valve PC cooking of stock/broths is over the traditional methods, check out this testing and verification by Dave Arnold at the French Culinary Institute at: http://www.cookingissues.com/index.html%3Fp=2561.html

The PCs get the job done in under three hours. Acceptable results often in less than an hour but a bit richer if you go an hour or so longer. I've used PCs on gas and electric burners, but I prefer using a portable induction cooker (PIC) because its digital power/temp settings and the timer-controlled burner give me near fire-and-forget ease of use.

I've sometimes taken stocks and broths out to 6 hours --- requiring one-timer reset on my Max Burton PIC --- but the improvement over two to three hours in the pressure cooker seemed so marginal as to be barely noticeable.

For folks who want their bone broths with more calcium, gelatin, etc. suspended/emulsified into the broth --- as you would get if you had the broth at a higher simmer/low boil than mkeys uses with the 24-hour stockpot simmer -- Laura Pazzaglia explains the pressure-cooker technique here: http://www.hippressurecooking.com/pressure-cooker-bone-broth/

But, for folks wedded to the 24-hour still simmer (almost sous vide) technique, the Caso seems like it might be the only induction-game in town for the PIC market, at least until the probe-controlled Paragon is released. Apparently, that same Bluetooth temp probe is also supposed to work with the newest GE Cafe and Monogram full-size induction cooktops, too.