I'm not a proponent of applying BRM guidelines strictly to small rolls that aren't too hard to replenish if you run bad and go bust. That doesn't mean it's okay to use the entire $30 to buy into only a couple of tournaments. However, I don't have a big issue with, for example, playing $2.20 or $3.30 tournaments even though you don't have 20 buyins which is the smallest number commonly suggested.
OTOH, if you feel it would take a long time and/or a lot of effort to get back to $30 if you go broke, then you'd be better served to apply a more conservative guideline, say 30 buyins, which would mean not playing anything over $1.
And if you prefer tournaments, stick to them. There's plenty of time to learn how to play cash after you improve your MTT game enough and to know you're +EV at low stakes and after you've accumulated a few spare dollars you can set aside for ring games.