Hey Rick, I saw that you found an O'neil drysuit for $350, nice. You can find polypropolene 'fleece' undergarments at Wal for a reasonable price. My fins were too small for the drysuit but I was able to sort of make them fit, ask Ron. Scubapro XL jetfins are only $70 on Leisurepro.
I'm not sure how much undergarments I'll need. You said not to underestimate the neoprene, do you mean that it does a good job insulating or that it doesn't do a good job? This suit is 7mil but it seem thicker and heaver than my 7mil wetsuit. Might just be because there are socks, and neck and arm seals, and a really heavy zipper. I didn't get cold
IN the water with my wetsuit. There was a little chill when the water first ran down my back, but after that I was fine. So I don't think I'll need much undergarments with this drysuit at Blue Hole. Now when we start getting back into 43* water in the mountains, that will be the test! The "fleece" your talking about at Walmart...is it like the old fashioned long underwear? Or like warmup pants/jacket, or more like sweats?
I really didn't want to buy new fins. I looked around at rock boots, and then canvas Converse tennis shoes, but wasn't sure that even they (when I got a large enough size to fit the over sized "sock") would fit my fins. So, for now, I got a pair of water shoes - similar to what I wear in warm water with my fins, two sizes larger. I did a quick check, and I think they will fit, but I'm looking at making the heel more secure. Right now, I think it might slide off the sock. I've never had any problems on my bare feet, or with the fin strap sliding off when I wear them in the summer.
I think the neck is a bit tight. I didn't get any directions/information with this suit, but have read that some "stretch" the neck seal over the end of their tank. Did you have any problems with your neck seal? Also, it came with a huge duffel/backpack bag, but I'm not sure how to store it correctly. It came folded, outside the bag, in the box, but I've read that you should not fold neoprene, or you will weaken the cells at the folds. I read where some drysuits you roll up, but not sure if that was just for trilam or included neoprene also. I thought I'd get a "care and feeding" guide for the suit written by O'Neill, and maybe even a warranty card. But there was no paperwork in the box at all. Not even a packing list or invoice. I do have an electronic copy of the invoice, not that it will mean a lot. But the price was right, and if it allows me to do a few of the mountain lakes and a few dives earlier/later in the season than I'm comfortable with my double 7mil stuff, I'll be happy. And I am hoping to learn more about them, so if I decide to drop a grand or two, I'll be better informed and experienced.
I won't try it on a night dive for this first dive. I want to get used to the feel, and the feel when there is too much air, not enough, and see if I have the problem of "feet first" (I kinda doubt it, since I don't think there will be enough air in the suit to cause that problem) and practice maneuvers to get out of that condition if it does happen. I'm planning (as of right now) not using it for buoyancy adjustment- but use my BC for that. What do you do? (Ron mentioned that you bought a neoprene also). Oh, I did get it off eBay. They still had some last I checked. I'm not sure, but I think O'Neill is getting, or has gotten, out of the Scuba Drysuit business.
I just put an order into LeisurePro for a wreck reel. I'm taking the Deep and Wreck Specialty Courses next month on Bonaire.
Even if she was not planning on being there, we could get her there! 
The only issue is if they are going to start tearing down her shop, and disable the compressor. I hope they do that during the week, but it's always a good idea to check during these uncertain construction times in BH! 
He had a nylon rope that was originally on the inside of his springs, but to make this work, he had to let out the rope, and the spring strap was 50% spring, the rest rope, and the fins were shoved onto the end of his feet! It was like putting a size 8 shoe on a size 13 foot, and I can't believe that these things did not fall off (in fact I think they did at one point). He made it work, so all was well, but I think he has found a better solution at this point as in.. different fins. 
