Probably only a few bucks.  I'm not really sure.  If it's in good shape and it still works, maybe $10-15, but that's pushing it.  Of course, I'm no expert...but hey, if it works, and you can play it, the LSL games are fuckin' hilarious!  Definitely worth playing it 

I agree with his price.  The only Leisure Suit Larry game that is worth more is the collector's set, which sells for around 30-40 I think.  It's a bit surprising, as a lot of the older point and click games tend to be in high demand and used to fetch quite a bit more than they do now (i.e. King's Quest series, etc).