Sit and Go bankroll

[arizona]

I was just wondering what a decent bankroll would be if I wanted to play sit and go tournements exclusively. I am assuming that I will be able to finish in the money %50 of the time (right now its a little lower than that, but I think I can improve). Any thoughts would be very appreciated.

[alekhine8]

Im playing the $10+$1 right now working off of a very short bankroll because I cashed some out already. I am trying tu build up to 25 buy-ins at $30+$3 ($825 total) before I move up. I think 25 buy-ins is a pretty safe number but I dont have any mathematical formula or anything to back me up.