I also ride all my bikes and consider myself a collector of sorts too. Most of my buys I try to get for what I think is a good deal (part of the fun) and consider resale value on all of them but rarely do this. Ceiling price is a case by case thing but when I consider that each bike I have individually won't get that much mileage, I don't want to spend a lot of cash. I will start to balk when price gets in the $1000 realm, and haven't spent that much on a bike in a while. I generally look at $200 or 300 for a good frame/fork.

That being said I will up the ceiling when I really zero in on a specific want. I'm currently trying to find a frame to replace a nice one that's too big for me. If I win the auction, that will push up to $500 for it, but hopefully selling the replaced frame will take a lot if not all of the sting out of that.