How many bigbets to play at a certain level?

I'm rather new to this forum. Been playing poker for around 7 month and been doing ok. What puzzels me is that the guys here at this forum seems to be good players... but still are playing low-limit. How big bankrole do u like to have to be able to go up a level? I want 300 bigbets to play at a certain level.

What about u?