peerthy.s costs might depends on many factors as for example complexity, time restriction, skill required (only coding? or others like art and audio?)
You'd better specify as many info as possible otherwise you might get a roughly hourly rate but it might not be matching the real complexity of the project.
Also adding more details you avoid unnecessary mail exchange.
For example you want a multiplayer game but some people don't want/can't develop it or you want a game for Android and iOS and the developer isn't interested on working on them, etc.