How much could did it cost to build CryptoKitties ethereum-powered game on blockchain?
The cost depends on what you are going to develop. I hope you have a proper business model to develop and not simply vaporware because the later will not be in anyway beneficial for the community.
Anyway the major costs are development, analysis, technical, management and maintenance. You need have a developer team at first and someone to manage the technical issues as well. Consider a public beta testing once the majority of development and auditing is complete.