I win about 1 in 4, 2nd in 1 in 4. So cash nearly half of the time, with some bad streaks now and then, but generally I play pretty tight and cash. Although I get greedy with winnings and play a $30-$50 buy in sit&go now and again and usually lose, or get lucky and cash right up. I'm working on discipline and BR management ATM ;-)
I say around 1500-2500 dollars. If you want to buy in 100 times then you must have 1500 bankroll. The rule of thumb according to my reading is you must have a bankroll at least 100x the big blind at cash game and can be reflected at tournament as well according to buy ins.