+1 for buying a plane that's already on floats. I looked at a 182 that had the Seaplanes West kit and a set of EDOs with 180 rigging that it had never been mated to. The owner swore up and down that he had all the parts for everything and it was just a matter of assembling everything. A quick call and some photos sent to Seaplanes West revealed that he had the wrong parts and, had I bought the plane without doing my due diligence, it would have cost me a ton of money and time (6 months or more to get the correct parts) to get this thing on floats.
Logic dictates that, at some point, people will have to convert landplanes into floatplanes to make up for the deteriorating fleet. While you could certainly take that on, I say leave that up to commercial operators that can write off the cost. If you can write off the cost, then I take it all back - convert away!
While I'm always after a good deal, I've come to realize that floatplanes are expensive and there's really no way around it. If it looks cheap, there's always a reason.