Personally, I would only use the Porsche OEM (which as JFP correctly says should be < $35 locally or $20 from Sunset or Suncoast Porsche). FWIW, there have been posters (on this board no less) who tried using the 'correct' GY or others belts only to find they didn't fit.
Though it only takes two minutes to replace the actual belt (once you removed all the interior liners/carpet, parcel shelf, front engine cover, etc.), you don't want to have to tear everything down only to find the belt you picked up won't work...
Good luck
