Great catch, it is the top three players who win. Given ethereum and the gas costs it can't possibly be any cheaper than this without making it centralized (no smart contract, just sending ether to a regular address).
Without a smart contract there are no guarantees you will get your money back if you win your game (thusly you have to build a lot more trust in a centralized game than in a smart contract game).
I'm an ethereum developer so I wouldn't know where to start "[using] STEEM".
Ahh, well thanks for the explanation. I'm a bit of an opinionated loud-mouth with no real coding skills so my opinion literally comes with zero description as to how to go about such tasks,
Sorry about that. :)
Anyhow I am sure there are several dozens of developers on steemit who would love to help you with this project if you desired it and looked in the right places. You could start in Whaleshares on Discord Come by and introduce yourself.
Also, if you're interested, have a look at our project #haveaheart.
Take care :)