From what I've seen of those I play with, it's difficult to blow through 2k BBs in a single sessions. As such, I wouldn't mind paying $30 for the inclusion of the 2k BBs on days when I'm low on BBs - but I wouldn't want to pay $30 every single session, and start accumulating bags of BBs I can't use fast enough.
There are those who have no problem blowing through 2k, but there aren't too many of them that I play with. Especially those who might participate at a tournament level.
So in short, a "forced" purchase of a bag of BBs with entry, would turn me away more often than not.
Every other week sounds like the ideal interval. I'd drive an hour every other week.
Geez, that's a pretty big risk and investment. I might be too scared to actually play with them!
You're going to need to spend a lot of money on mounting gear for them too.
All it takes is someone walking into a chicken wire fence that's out of focus for the NODs! *cough*shelledpants*cough*