Dont think that you wont lose much on having a pvp gambling site. You need to lose some btc on promotions, it is always hard to start a pvp gambling site like peerbet or poker game.
Most new gambling site will always lose at start for the promotions, then they will get some profit after several times (could be a month, 6 month, a year or even more)
At least you need to prepare much money for it till you have good traffic, then you'll enjoy your profit
Of course I am going to need to pay for promotions etc, what I mean is that I won't create a simple dice site and have a whale empty my house bankroll on day 1 :p
Try out the moneypot API, you'll have to split your profit with moneypot and their investors, but in exchange, they take care of your site's bankroll, so you won't have to fund a bankroll and worry about whales emptying your bankroll.