how much can you sell it for? Not much can you? The ps3 I think is releasing at 60 dollars though I could be wrong.
New copies are selling for 20 bucks now. Atleast here. So unless you Ebay not sure you can get a lot for it.
I played it on the PC. so, I'm not going to play the PS3 version but.
The best download Content is Overlord and Shadow broker. That will cost you about 14 USD... I think not sure what the price is if you're not in U.S.
I'd just buy those 2 DLC and kasumi if you really want an extra character if you don't plan to use her don't buy this... the second play throughs are fun I played in Hardcore both times. I started to play Though insanity and I don't really like it, because I feel they just upped the HP too much. Not their strategy. And it feels like I'm wasting time shooting a sponge.
Also the PS3 version could have technical issues as some ports have. Though that obviously is unknown at this point
My advice is to just wait until you want to play it again. I'm not sure how much more this game will go down in price so I don't think the trade in value will get hurt much more.