If you have patience, discipline, good money management and selections you can start with as little as 5k and start seeing some nice returns within a few months. 99% of bettors don't have the head-game, let alone the smarts to beat the juice and books. And the ones who do may not have a huge roll to put down or don't feel comfortable risking 100's or 1,000s of dollars a game which leaves a tiny fraction of people who can consistently make money at this year after year (I am not one of them).
And I usually like to deposit around 1,000 and most always make the terrible decision to bet too big on deposit day and bet on shit I know nothing about like Soccer, foreign hockey or euroleague.