I got the spare from Tire Rack, with shipping it was about $101, $10 to have it mounted and a new valve was included. IMO, a 17 year old tire is most likely got a bit of dry rot. The distances between cities here in the desert South West can be pretty vast, and I'd just rather not worry. It sometimes gets kinda hot here.
$110 is cheap compared to almost everything else on my Boxster.
The replacement tire looks so much like an old VW Bug tire. Took me way back.