These are great boats. A new head gasket is not a huge problem and can easily done by yourself. If you need some advice for that, just email me at
tvhoek@hotmail.com . The advice of Zedz is good. Pull a head of and see how the cilinder, pistons, valves and rings are. If these are good, you can change the headgaskets and run that thing for thousands hours.
$6.000 is not to much for a Barefoot (which year?) with a bad engine. If the engine is the only problem, buy it. And rebuilt the complete engine. Then you have a problem free boat with 350hp for years and under the 10K!
I've just rebuilt our 454 in our Barefoot. Took me 4 weekends (complete from taking the engine out till last weekend from test drive) and about $700,- . The major part of this money was due a electronic ignition (instead of points) and gaskets (all new gaskets). We checked every piston and bearings (no problems) and repaint the whole engine. No problem, even not if it's your first engine to rebuilt! These things are fairly easy to do.
You can contact me for advice! Try to get the boat cheaper but 6.000 is not to much. A Barefoot trows a good wake and weighted even a huge wake.