They usually come up on Ebay every once in a while. I got a baby seat in really good shape for my 6 month old for only $65 bucks not long ago. Once you get any of the Porsche infant/toddler seats, you can just cut off the belt buckle that inserts into the deactivation bar below the pass. seat, and then you can use any brand booster seat you want pretty much. After you install the bar, you will have to get the deactivation bar programed either at the dealer or find someone who has a PWIS or PST2 Porsche computer.
A pal of mine who has the computer programmed the deactivation bar for me so that the car recognizes the deactivation bar, and now my car is good to go as a baby transporter.
You can get the deactivation bar from Suncoast Porsche:
http://e-partssales.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=P&Product_Code=99680308302&Category_Code=986seat
