I bought just the one for about $150 from pelican parts (keep in mind I have a 2003):
http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=996-606-106-03-M14&catalog_description=Camshaft%20Position%20Sensor%2 0%282%20per%20car%2C%20sold%20individually%29%2C%2 0Boxster%2FBoxster%20S%20%282003-04%29
I think for your 2002 you're going to need:
http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=996-606-106-02-M14&catalog_description=Camshaft%20Position%20Sensor%2 0%282%20per%20car%2C%20sold%20individually%29%2C%2 0Boxster%2FBoxster%20S%20%281997-02%29%2C%20Each
I'm no expert so please double check all this before ordering ;D and any pictures would be great. I just received my sensor today so I might try to take some pics myself of a bank 1 sensor replacement. I also picked up the Bentley Boxster repair manual which should be arriving in the next few days, I'll check that for pics too.