Are you talking about a web application?
Writing just the database portion of the application should be less than $500 but to do the database AND the web site I think $500 seems to be a good quote. If you wouldn't mind about the professional look you could get it for less for sure because not everyone can make a beautiful interface.
Make sure the specifications with screenshots for this application are written before you pay them to make sure that you both agree on what will be delivered.
If you want to save a little bit you could have someone design the look of the application and then have someone else (think about an individual working part time at night) do the logic in the application (database and code to display and manage the data).
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