I just sold an alum MacBook today on eBay for $435 (C2D, 4GB RAM, 160HDD). A bit off topic, but you're accurate in how much your machine is worth 😉
Edit: As a matter of fact, now that you've installed 8GB RAM you could probably get closer to $500 for it. Personally, I am not getting rid of either of my alum MacBook's (not saying you're trying to sell yours either). I really like them. They have been nothing but great for me, minus a few minor problems that were an easy fix.