www.tirerack.com, dude! I bought a set of Kumho's for my 97 and got them for 540.00 delivered.
Be sure not to buy the cheapest Kumho's though because they require rotation to keep them quiet and we Boxster owners can't do that.
But, this is a can of worms. Everyone has preferences on tires and feels strongly about it! I just chose these because I knew I had lots of repairs to do and just needed basic rubber. But, everyone who sees them and knows tires says "those are good tires! Great choice!"