Hello, I noticed you have this job posted twice. The screen shots you have posted on the web site are very nice, the app is clean looking, easy to navigate it, it seems. Is it yours or do you want something similar? If yours, do you need enhancements, changes? If not yours, perhaps you should consider taking to its developer to get a copy tailored to your needs, if the app works fine, if you can get a hold of the developer and if your budget will permit it. I may be staving myself, but my main concern is to have the FMP user satisfied, even if the satisfaction does not come from me. One thing I did not see on the app shots was a field to have the locker owner/renter sign when he/she comes to the place.
Your budget is a little low for all the time needed just for the UI part, not counting the scripting, etc, but I am very passionate regarding FileMaker Pro.