I blew my own insulation in with the help of my wife. I had 4-5 inches of insulation when I started. After blowing 40 bundles in I had about 30 inches of insulation. I used cellulose. Total cost was $200 because I had coupons. Without coupons it would be $300. My house is 1500 square feet for reference. It only took me 1 hour of time. Questions I would ask for those giving you bids: Approximately how many hours are you planning? How many employees would be working during this time? How many inches of insulation will be there when complete? If you have 1500 square feet and they are adding 24 inches it would be $300 for the materials. Add about $25/hour for each employee they state. For 2 employees taking 2 hours and approximately $300 in materials Anywhere near $500 would be a reasonable quote to me.

If you use a whole house fan, there is no point in having a sealed attic system. You need an old fashioned "open" attic system. You want the hot air to vent out through the gable ends. You have a grate in a hallway that opens and the (presumably) cooler air from outside the home is drawn in through the open windows through the home, through the grate, and exits through the attic vents. WHole house fans are NOT compatible with conjunctively using your AC system. And, as I mentioned, the exterior of the home must be cooler (and less humid) than the interior for the whole house fan to be a viable option. 85° is pretty hot for most people, and I presume you're in the South where the humidity is also very high. Southerners LOVE their AC for a reason and long ago abandoned their whole house fans except for about 15 days in the spring and fall. WHole house fans are like owning a convertable. It sounds like a good idea, and if you live in a place like San Francisco, it probably IS a good idea. But, for folks who live in most of the rest of the country, there just isn't enough ideal weather in the year to be able to fully utilize that top down motoring.

OP here. My roof is in great shape so I won't be replacing it any time soon plus it has some interesting curves to it so adding rigid foam and sleepers over the roof deck might be more trouble than its worth. See pic: I do have the gable vents and the giant vent over the porch so I think ventilation in the front part of the attic (the shorter knee wall in the original picture) is ok. I think what I've decided to do is to add soffit vents on the back of the house (where there are no intake vents). Then I'll install a foil radiant barrier on the bottom of the roof deck in all of the accessible attic areas. I will pull down the wood paneling stuff, add rigid foam between the studs in the knee wall as well as the roof rafters, and install sheetrock over it all. Its all 2x6 so I should be able to get 4 inches of foam (R20 or so) in there while still leaving a 2 inch gap for air flow under the roof. I found a guy on craigslist selling 4 inch closed cell foam at 75c per sqft. I've also thought about being cheap and just using fiberglass batts (r16) with baffles on the roof deck instead of foam. That would cost r4 but save quite a bit of money. So long as I make sure I've got a good air seal with the sheetrock and plenty of ventilation, after that, its all down to r value right? I've also essentially given up on the thought of spray foam on the roof deck. That would cost in the neighborhood of 5k plus the cost of ripping off and reinstalling the sheetrock.

I have ALWAYS stored items in attics. I would take up the storage area decking, put faced fiberglass batts under it, replace the decking, and then put thicker fiberglass elsewhere in the attic. I wouldn't use cellulose at all. It makes a mess, and it compacts over years. Six inches of insulation in that area may not be optimal, but it's better than no insulation. If the area is a small percentage of the attic square area, the additional heat loss will be minimal. Just store a bunch of blankets there. :)