Anybody using a BTS for debugging?

Hi, It seems like a BTS is required in order to really debug anything one develops with osmocombb. I'm still looking at implementing SMS. However the only off-the-shelf option seems to be USRP which is about $1,000 right? Is this going to become a very expensive hobby or are there cheaper options here? Is there a way to bypass L1CTL on the phone and feed the data in to, say, openBTS? If not, it would seem useful to hack such a thing up... Gianni