Sorry, but you're asking way too vague of a question to get any meaningful feedback. To say it depends on the complexity and functionality is an understatement.
Do you need to have any back end servers to manage data? Data/document storage and transfer? Web integration or completely stand-alone?
You could spend anywhere from $10,000 for a very, very basic app that's anything decent up to hundreds of thousands of dollars. Then you have to factor in marketing, support, etc.
Sketch it out, listing the functionality you want. Put it in three categories: Essential core functions for the app (the must haves in version 1.0), the next level functions you'd like to integrate once this proves to be useful and at least potentially profitable and finally the ultimate function list.
Then sit down with a developer and discuss things. The more detail you bring to the table, the more accurate your cost estimate is going to be. If you just waltz in with a vague "I want an app to do X" idea, you're going to spend a good chunk of your budget on the design and functionality wireframes. Instead, get out your pad of paper and start your lists. Then take those lists and do a rough sketch of what the screens look like. Can you come up with a flow chart of functionality? Do you have graphics in mind? Do you have them already or does your developer have to do them? Or a third party?
Be precise in your contract. What exactly are they doing for you? Bug fixes included or no? If they're included, how long do you have to report them for them to be fixed or until you have to start paying for additional work? Is this a flat fee to develop the app that you sign off on once wireframes are done and finalized? Or is this hourly?
What about payments? Milestone payments? Open ended monthly payments for work performed?
Be sure to get your contract to specify that you are the creator and own all the intellectual property and are entitled to all graphics, source codes, etc.
You'll get a feel for pricing once you can answer the question of "What is this thing and what does it do?", then sit with a developer or two