Against all advice, I think it’s fair for me to give you a very rough idea of the costs involved in building a web application. The following information is always subject to change, and is intended only to help you do very general first-pass planning. (For example, if you imagine a web app to take $300 or $30K to build, the following will be useful context.) I’d be glad to give you a more specific idea of what I think your project will cost, once we meet in person and I have a chance to learn more about your needs.
My rate during spring 2014 is $25 per hour (extremely low for Rails developers), but I’ll plan on quoting you a fixed price for your project, once we’ve met enough to understand its scope. I believe that a fixed pricetag is more protective of the client, can help to keep me as developer honest, and will make it easier for you to plan and budget effectively.
Each web app’s needs are different, making estimation difficult, but you can expect it to cost between $2000 and $10,000 to bring a small application from initial idea to usable, polished prototype.