Not really. I'd look around and see if you can view completed auctions on eBay, but it really depends on who and what are on the market at the time.
I try to think of things in terms of how much I want them or what value I'll get out of it and what my budget is, plus condition, specs, etc.
It's a pretty personal decision anyway. What might be worth a few hundred to me because I really want one might not be worth much to you, if you already have one or if you just don't like that kind of system, etc.