It really depends on the skill and expertise of the developer, his geographical location, complexity of the project and details, etc. Expect to pay around $50/h for a good developer, and twice or three times for really good freelancers in western countries. The choice comes down to how much you want to spend, how well you want the app done, and how quickly. You can find someone very cheap, but don't expect it fast and well done.
As for your specific app idea, by what you described, it does not look like a very complex app. If I had to ballpark your idea, I'd say somewhere between 120-150 hours, but without detailed specifications and functional requirements that can be just that, ballpark.
Keep in mind you also need a good designers, don't expect the coder to be able to do that. If a coder tells you he's also great at design, he's most likely either lying, or not a good coder