If you want to earn money, but only starting, play freerolls to understand your qualification. After that go play minimum buy in. Playing good and being in plus, you can go to bigger buy in, but your bankroll must be bigger than buy in for 500 times.
If you playing for fun. Think how many money you can spend for a month(or day). Think as you go to bowling, cinema or hockey. It is fun for you and you spending.
It is your bankroll, but spend it with many piece (not in 1 game)