I generally just put $5-20 in and play for fun. I am not one of those crazy people who get in the $50/100 tournaments b/c you beat your buddies in fantasy every year in your worker league. People quit their jobs and do this for a living. They gamble 4, 5, 6 digit dollars a day on these sites. They are considered "professionals" b/c of their bankroll and stats they use to determine the best possible scenarios to win b/c they have so many lineups.
If you are thinking about putting hundreds of $ you don't really have to spend onto this b/c they "match your bet".... (which also has fine print. You don't get that money right away, you get $1 for every 100 "points" you get on that site for winning/placing in leagues. So don't expect to deposit $50 and have $100 to spend.)
....then read that article. last year I put in $10 on FanDuel, got it up to $100 then thought, "hey shit, I have been doing good, I can win a shit ton more!" and lost it all in 1 week.
I of course got in it again but only put $5. If I lose it, I lose it and I am done.
No seriously, if you are going to gamble, at least be rational and pick something where you have the best odds. Winning this stuff gets harder the more 'whales' you have entering it. Just go play craps or something.
Just realize you are going up against Wall Street quant types who have PhDs in mathematics or computer science, and sometimes both. Winning has far more to do with understanding market exploits and working spreadsheets/data tables than knowledge of football. It's only a matter of time for the government to step in and regulate because it's hard to distinguish from gambling.