Hello,
there are 3 different camshaft sensors available (M 660 = OBD2):
996 606 106 01 (M 660)
996 606 106 02 - (M 660) 98->02
996 606 106 03 - 03->
You'll need the last one, because you have a 2003 car.
And because it's a 2003 i think your car has 2 camshaft sensors.
At ebay you can get one for about 20-40 Euros (185 - 370 SEK) like Mezger and other after market manufactureres or a Bosch one for about 90-100 Euros (835 - 927 SEK).
1.000 USD is much to much for that repair.
Regards from Germany, Markus