I'd look for a used 2.5 merc. People around here hate Mercs, so they tend to sell cheaper. The 2.5 is a better bet on spending money on because they don't have th chrome bores, if you score a cylinder, it can be bored. I've seen factory rebuilt 2.4's start flaking the chrome off the bores, when we went back to the rebuilder, they told us the engine had been over heated and it wouldn't be covered by warranty. If your 2.4 motor uses the single cylinder trim system, the race guys like using that type of center section, so you could part that motor out and recover a little. You can find decent deals on OPti's for under $3500, but with no warranty on those things, they can get expensive if they need anything. I know Yamaha's bring a premium down in your area, they are more likely to be stolen as well( they end up in the islands)
check this site from time to time, suprisingly, there are a couple of deals on here for some Yamahas, but they're ususally alot of Merc's on there
http://www.charlestonfishing.com/for...ds.asp?catID=3