Please give me some thoughts on where to look. The closer to the north side of Chicago the better. Or are there some online only places I should check out.
If you can get up to Mundelein you must pay Sho-Tank a visit. He (Matt?) always has used but very presentable acrylics in the front of the shop at less than half or more from new retail. Most are 60 gal+ with some monster 300 gals that I've seen once in a while. Most with stands. Will Lutman could probably speak on the quality of Sho Tank's used Acrylics.
Old town aquarium offers acrylic tanks from Innovative Plastics. I have an all in one tank from there - recently I have seen several for sale on CL at great prices.
I like the truvue brand for pricing myself, not sure of local vendor but can order online.
in a 90 probably not huge savings, bigger tanks they really seem to be priced right.