How to validate your business idea for less than 100$ - Part 1.

Last year I had an idea about an online portal for collecting bars and restaurants menu in one place and compare their foods and drinks, so I wanted to create a prototype and send it to a startup incubator. I spent months learning and developing a Ruby on Rails webapp with tons of code and headaches, but the point was that nobody wants it. I litterally wasted my time, but what if you could validate the potential market for you startup BEFORE creating the prototype?