Hiring programmers to write code has a lot in common with hiring artists to make art. They all call themselves artists, but unless you're in a position to really appreciate what they're doing and how they're doing it, it's hard to make sound decisions about them.
My prices are generally on a fixed price basis, clients prefer this as it gives them peace of mind as to how much the project will cost. Previous projects have started with a Feasibility Study where I will analyse the project, design a solution and propose a fixed price for development. This exercise will define how the solution will be built and give a clear specification of what I will build. It will also help you realise how feasible the project is and how the solution will work. To give you an idea of rate (I live in London) I charge clients £400 a day to be in their office writing software. This number is negotiable and will be less if the project involves remote working, flexible timescales, appeal of the project etc.