The application is basically an exchange platform with the ability to chat with one another. So every buyer and every seller has to put some information when registering to the app that will make the transaction easier for them because it has to happen face to face. So that information will locate approximately where the buyer and the seller are so they will be able to meet after chatting together to arrange the meeting. With this approximate location, some advertising might be added depending on each user. The goods sold have to have some information including maybe 1 or 2 pictures.
This is the basic idea, more information will be giver if you're interested.
This app must be easy to use so intuitive and simple.
I want it to be reachable from any smartphones.
The budget will only depend on your performance if I like what you're doing a bonus could be added and even a partnership could start.
Thanks!