I, too, want a very deep cast iron soaking tub for our new master bath. I'm going with the sumptuous Kohler Tea for Two 5.5'. It's 19.5" to overflow (the deepest I could find) and holds a whopping 105 gallons! It can be dropped in, undermounted, or installed in an alcove. I'm trying to tell myself that I'm not ruining the planet by getting my dream soaker that guzzles water. I laid in it at the plumbing supply showroom and didn't want to get out. I don't know what cost prohibitive is to you, but this one isn't cheap. Kohler lists it in white for $2125, but Faucetdirect.com has it for $1434. Oh, and I should mention a warning from the showroom saleswoman. The tub weighs more than 400 pounds. She told me that delivery and install will cost a bit more (whatever that means) because it is so heavy. Installing in on a second floor room can be tricky. Ours is new construction on the first floor so hopefully it won't be too difficult to deliver and install. Here is a link that might be useful: Kohler Tea for Two

Congrats on bath remodel! and on choosing cast iron - Kohler has excellent products and user friendly site to determine what they have that will suit your application I recently put in a Memoirs tub & am very happy with it I did a search on cast iron, 60" and alcove application (assuming that is what you are doing) - click link below & make certain to click on the SPEC portion of the tub you are interested in - this will give you the actual basin size, gallons used, dimension to overflow For instance their "Steeping bath" has a basin or bath area of 45" x 19" while the memoirs basin is 43"x23" I like having more width - Good luck! Here is a link that might be useful: kohler cast iron

My acrylic Bain Ultra air tub was set in a bed of mud with a piece of think plastic between the mud and tub. This was done for the ease of removing the tub if ever the need arises. It's as solid feeling on the bottom as my husband's Kohler cast iron tub. As for cleaning, that's a different story. You're not supposed to use anything abrasive on acrylic. Believe it or not, Scrubbing Bubbles is considered abrasive :( That's been my go to tub cleaner for years. To clean my acrylic tub RIGHT, I use Gel Gloss. It's a pain (literally!). You spray it on, let it sit, buff it and let it dry and then wipe the residue. When I'm in a pinch for time or physically limited, I will use Scrubbing Bubbles. There are very few non abrasive cleaners out there. One Bain Ultra suggested was Lemon scent Lysol. NOTHING works better than Scrubbing Bubbles!

In my Kohler cast iron shower pan, I use something called R.O.G.3 Its a spray. I can't remember how I came across it. Supposedly it is recommended by Kohler. It works well. I wash my light gray shower pan about once every 3 months. I am the only one using it and I don't go barefoot. So it stays very clean. I could wash it more often, but I can hardly tell the difference. I clean the walls about once or twice per year, because I wipe the entire shower down after every shower with a microfiber auto detailing towel that I got at The Rag Company. Wiping down everything prevents any build up of soap and keeps all areas from getting moldy. I turn my fan on, and run about 30 minutes, when I start my shower and have never had any mold issues in the bathroom. Nothing steams up. the towels I use for drying are: edgeless-avalanche-20-x-40-super-plush-drying-microfiber-towel I hang it over my glass shower door and it dries beautifully. When I wash the microfiber, I wash on hot water with only other microfiber products. You don't want to wash microfiber with cotton, etc, because the lint from these other fibers are believed to "clog" the grabbing capacity of the microfiber. I used a squeegee for a few months and hated the process. A towel is SO MUCH easier IMO.