What's a competitive PPC rate?

Hi, I am looking to rent an ad space in my public transport connection search application for Prague. It's got 2500 users and 4000 views per day.

I wonder what's a competitive pay per click rate that would convince advertisers to use that space?

Please note that I only want to show one campaign at a time in the app, there will be no keyword auction system. For technical reasons. Perhaps price per click should be fixed.

Poster :