Much depends on who you are and what you are really looking for. Counting what I have now and the one I sold in February, I have had five 1999s that were all originally purchased for under $5,000. None were perfect. I have been happy with all five. (My $3,500 2000 S is not quite so happy, but that's another story.)
I buy them because: I like to learn and work on them myself. I love to drive them. I like to make them eventually look good, but I am not trying to impress anyone with my 17 year old Porsche.
My first Boxster was $5k. It had some minor hail dimples and the top had to be operated manually. I did minor maintenance such as oil changes and replacing a few suspension parts. Never had any serious problems and sold it for a little bit more than I originally paid. Probably paid about $1,500 in maint and mods/clean-up over the year and a half I owned it.
My most recent purchase was about $2k and needed a little work:
Oh no, another...
In between there's:
This & That
...and another I haven't really posted much about yet.
My point is, Yes, you
can get a {potentially} good Boxster for $6,000. It may need some work to get it up to par, but if you can do it yourself it can be affordable and rewarding.
You can get a bad one and pay a lot more even if you try to do everything right:
http://986forum.com/forums/general-discussions/62744-hammerhead2501-what-happened.html 
You've gotta ask yourself one question: "Do I feel lucky?" Well, do ya, punk?
