Looking at the Texas market on Craigslist, I see several cars in the price range that could be good buys. 1999 models are fairly plentiful and can be a good reliable car at an affordable price, but all 986s will require a maintenance budget to keep them in good shape.
If you have tools, a little experience, and a place to work you can save a lot of money. If you don't, you will need to spend $100/hr or more for a good mechanic to keep it in shape. What you can afford to buy and what you can afford to keep and drive could be two different things.
If you are willing to spend your money on a car that will have lots of minor electrical issues, worn out suspension, and an engine that is about to fail, then don't worry about having a knowledgeable Porsche mechanic look at the car before you buy it. Otherwise plan to have a PPI (prepurchase inspection) done.
That and much more is covered in the:
http://986forum.com/forums/boxster-general-discussions/14685-thinking-buying-boxster-must-read.html
So... what oil is the best and which replacement IMSB should you get?