RPS is very easy to make provably fair. In fact I do it all the time. Here's a good example of me playing in a provably fair way (for both of us) just using this forum:
https://bitcointalk.org/index.php?topic=1588904.0 and includes a lot of explanation of how it works
I didn't know RPS could be provably fair, that makes things a lot easier to add in a game. I would really love to make a website with provably fair RPS in it, you wouldn't need any bankroll at all, just make people gamble against each other in a provably fair method and you would make money from rake instead of spending any money yourself.
However, there would be development+design+marketing costs and as a person who has less than 5k dollars in bank account all I can offer would be cheap third world development+design and wouldn't be a good job done for that amount of money and on top of that I wouldn't have enough to market it.
People think when you can code a casino the job is done, that is literally just step one of creating a website bustabit didn't became bustabit in one day.