At first blush, I'd say that $200 for a 55g without a stand and probably needing to upgrade filtration right away would likely be far too much. If it had some nice lights and was a high-end tank, that might sway me. But since most used tanks are your standard glass tanks, they go for $1 per gallon. If it was a nice Oceanic, modern-decor-style, or acrylic tank, then they would likely go for much more.
I'd go for the 75g instead.