Ruby on Rails testing platform

I want to build a platform similar to [login to view URL] To cut to the chase, i want a platform where IT people can test their skills solving problems. their solution will be tested against pre-provided use cases in various programming languages( C#, ruby, java, js, python...) These unit tests will be handles using various pre-existing gems. The design is 90% complete so, all we need now is the code and integration. Give us a price! Technologies involved: Ruby & ROR, Javascript, Bootstrap, Jquery, Haml, ruby gems, git, payments(paypal or wepay)