That 8.95 is the cheapest I've seen. Shipping kind of kills that though. I'd just go to your local Sram dealer and cough up the 15 bucks to have them order you one.

Was the crankset new? If it is, you're definitely missing parts and you shouldn't have to pay for them. If you bought it used (I recently got a good deal on a set of Omnium track cranks that didn't have the self-extracting cap), then you're up a creek. I ended up finding somebody that had broken a set of Truvativ cranks and he gave me the self-extractor cap for free. Ask around.