Hi Jay.
From reading a lot of post about the subject, it always comes to the OEM pump.
A lot of people hade bad expiriance with replacement parts. Again, based on posts in this forum.
Suncoast parts sale the OEM for $300.
Water Pump with Gasket:Porsche Parts & Porsche Accessories - Wholesale Porsche Parts & Tequipment
From my expiriance ( and this is where I buy most of my parts) sunset imports in Oregon are usually even cheaper. They don't have an online ordering website, so I suggest you give them a call or shoot them an email.