It depends. BR = all the money you have for poker, no matter where it is and how it's split up. As a simple example, say I have a strict $1000 budget and will never put up another cent. If I deposit $25 to a site, my BR is still $1000.
If I use a 30 buyin guideline, my $1000 BR divided by 30 = $33.33. Note that this doesn't take into account whether I'm good enough to handle this buyin level. This obviously isn't a smart thing to ignore, which is why it's a good idea to start at the entry level and to work your way up as your ability and BR grow.