Here in the Northeast I would expect to pay around 10K for a "good" not great one. In the 70's you had 2 options, the Beetle (Ball Joint Front End) or the Superbeetle (Strut Front End). Beetle is more desirable than a super. I would stay away from any car that has:
Fuel Injection, Autostick, Semi-Automatic Trans
Rusted out Jack Tubes, Rusted out Running Boards, Rusted bottom of spare tire well, Rusted heater channels, Rusted out battery tray under back seat, Rusted floors.
Rotted heat exchangers on the exhaust manifolds aren't that bad.
Any car that passes the above has either been babied and garage kept, no winter use, etc. or has already been restored. The former is rarer that the latter. A friend outside Buffalo, NY just bought one in Florida for about 10K and it needed tires and brakes but body was solid.
You will also need to find a VW shop that will work on air cooled models. These are also getting harder to find but still exist.