It depends on your variance. Obviously the tighter you play, the less often you'll get involved in marginal situations and have smaller swings, thus not needing as large a bankroll. Though even then, if the game plays crazy, and you often have to put your whole stack in pre-flop you'll need a larger bankroll. For most people though, I think something in the neigborhood of 10 buy-ins should do it. I would say at least $2,000 in this case maybe $3k.