I'm in IL and also looking for boxster S but with tiptronic for below 17-16k and to be honest it is really hard to find one that has less than 70k miles and newer than 2001,
They either old or have 6 owners or were were bought on auctions and sold by shady dealers
I guess you can always get lucky and find a perfect one for great price but it can take few weeks of feew months...