Your project must have a well defined scope.
If it doesn't, we can help you define the parameters a little better and build a clickable prototype of what you want, in an iterative process. We will bill you on an hourly basis for this service.
This article can also help you understand exactly what you/we need to have so that we can provide you with sensible time/cost estimates.
We recommend Mocking Bird or Invision for articulating you concepts visually.