That totally depends on, what games you want to play. It also depends on, if the money in the poker account is supposed to be a bankroll. Lets say you like to play Sunday Million on PokerStars 1-2 times per month, and in between this you dont play at all. Then the money needed in the account is the $109, it costs to buy in, and not a penny more. Then if you dont cash, you deposit another $109 next time, you want to play, and so on.
If on the other hand you like to play every day, then you likely want to have some sort of bankroll or budget sitting in the account, so that you dont need to constantly make new deposits. If its just a poker budget until the next paycheck, maybe its enough to have something like 20 BIs for cash, 30 BIs for SnGs and 50 BIs for MTTs. As an actual bankroll though, meaning you do not want to deposit again, then the numbers are more like 30-50 BIs for cash, 50-75 BIs for SnGs and 100+ BIs for MTTs. And of course this can only work, if you are a winning player. Losing players can only have a budget not a bankroll 🙂