Develop an iPhone application like bloons tower defense 4

Currently there is a very popular app called btd4 on ipad/iphone. It is a tower defense game. I wish someone can create a similar app with the following: a) upgradeable towers b) easily customized maps c) easily customized enemies speed and hp d) the whole documentations Basically the graphics ARE NOT important. I just want the logics behinds. And wish you could make a very intuitive documentations on how to customize the game. The budget would be $100-$200 Thanks.