So it turns out that I already own a small rack system, or at least something that can easily be turned into one.
Salamander audio rack:
http://www.salamanderdesigns.com/pro...5-5125e28270f2
The shelves are infinitely adjustable in height because the "legs" are gigantic 3 foot long bolts and each corner of each shelf has big nuts that you can thread up and down to set the shelf heights exactly where you want them to match any sized tub.
The limitation is that the legs take up some space so the workable area is only about 19"x16". The biggest tubs I've found that will go in here are taller IRIS 32 quart ones (https://www.amazon.com/gp/product/B0...=ATVPDKIKX0DER) which are 18x14.5, and I think I could fit three levels of these by removing one shelf or do four levels mixing taller and shorter tubs. I can also adjust them over time if my needs change. I think the 32 quart tubs would work for Hognose, most Kingsnakes, Sand Boas, male Ball Pythons, and youngsters of many species as well as Leopard or Fat-Tailed Geckos.
Note that if you know any tubs with bigger floor space that will fit in 19x16 please let me know! The 19" is pretty much a hard limit, and wider and the top of the tub won't fit between the bolts. You could potentially stick out slightly to about 16.25" the other way I think and be OK, you'd just have a little bit of exposed lip.
Just add some heat tape and a thermostat and I'm in business! Yay for reusing stuff you already have and not having to spend money. I have a spare thermostat too.