It would be real tough to get an estimate on that right now because of the price drop; also, lots of rumors about BC coming for all PS3s in an update - your hardcore gamer, looking for backwards compatibility probably has heard that too.
Total estimate - but if you were to sell it on Ebay - maybe $225; less if you use Craigslist. Again though, it all depends on how much people still value the ability to play PS2 games on their PS3.
Here's a good auction to watch, to get a rough estimate (remember to factor in shipping costs):
http://cgi.ebay.com/Sony-PlayStatio...m2ea73d1992&_trksid=p3286.c0.m14#ht_809wt_966
This one also comes with the 60 day warranty too though - people would definitely be more apt to bid on this one.