I bought a 1971 22-2 flatback last summer for $4000. It had a nicely maintained 150 hp Evinrude Ocean Pro, a nice tandem axle aluminum trailer with new hubs and tires, and was solid and ready to fish. The boat was from the Tampa area and had been on craigslist for months. I'd guess that a reasonable price for a similar hull without motor and on a poor trailer would be more like $2500.
OTOH, if you buy a vintage Aquasport with the thought of restoration, you're probably going to be spending $10 K or more on the job, so a few hundred here or there on the original purchase is easily lost in the noise.