We've got a used 1991A1, used, in the shop right now marked $435, but for what it's worth, I would guess about $375 max. I would offer to pay $350, maybe a little less, since I *think* that one has 3 or 4 magazines with it, and I would pay about 15 or so a magazine for spares. (350 - 15 - 15 = 320 Or 375 - 15 - 15 = 345.) But if you have a drawer full of 1911 mags, that might not be a selling point for you.
Of course this is all conjecture, since I am not really in the market for a Colt 1911, since I like the Kimber guns a bit more. Might be the fact that my roommate has a Kimber Ultra Carry that is the cat's pajamas....
Anyway, you might find prices higher or lower depending on where you are. Just some more food for thought...
TR