on eBay you can find around $20
I saw a few at $20 but I'm not entirely sure they're working right now. One took his listing off while I was looking at it actually :/
I'm not horribly concerned with it being done soon but I would like to get the iPhone I just bought unlocked as I have absolutely no phone at the moment. I guess my other option would be to just get a prepaid sim with AT&T (probably AIO Wireless actually); I was planning to use the $30 plan with T-Mobile.