The most common rust spots for the 912 are, unfortunately, in the front suspension and jacking points. The front "pan", which holds the gas tank, the spare, and the front suspension, often rusts because it also holds the battery. The second worst rust spot is under the rear window (esp. at the corners), caused by a bad rear window seal. Fixing this usually requires some reconstruction of the window area. The other common rust spots are fairly easy to repair, esp. if you can weld.
Trying to find even a nice shell outside California for $3000 will be quite difficult. Many, if not most, of the cars came here originally. I'd wait until April and continue to save until then. It's much easier to find a reasonable car in the $5-8K range, which will run a lot less money to fix up to a nice standard than the $3-4K cars.
If you do decide to buy in California, the best place to check is
www.craigslist.org/car. There's a $3000 '67 in San Bruno (near SFO airport) right now. There are four other cars (three '67s and a '69) for sale, as well, all for under $8000. The '69 is in Sacramento (two hours NE of San Francisco), the others are within a hour of SF.