Cheapest way to get a keyfob+programmed?

searches reveal many threads of people arguing how the keyfobs work, without much in the way of results.



but basically, what's the cheapest way for your average schmuck bmw owner to get a keyfob for their car?

get a "blank" one off ebay and get it programmed? can you program it yourself by sticking it in the letterbox or something? can any dude with bmw coding software program it for you?



buy any old used one and have it programmed?



or do you ABSOLUTELY have to buy one BRAND NEW from the dealer?



and what about comfort access keyfobs? i know you can get a regular old keyfob programmed and it'll work fine....minus the comfort access bits.

and apparently you can get a generic CA keyfob and get generic programming and it'll also work.....minus the CA bits...

but how do you get a CA keyfob working with CA features?



i ask because the e91 i just got only came with one key, and new-from-dealer comfort access keys are priced around $500 with programming, yikes!