Based on observations, your particular product/service and many years of attending Oshkosh, if I was an exhibitor that was directly gen av related, I would not get a booth in the Fly Market. The FM is like a Bazzar setting, the kind you would find in the Casbah in Tangiers(been there) or in the West Bank of Jerusalem(been there too). It's certainly a fun place to stroll around for an hour or so and see what's being hawked. Mostly the booths are non-general aviation related, things like Tilly hats, leather belts, model airplanes, airplane parts in boxes and aviation books and memorabilia, plaques, posters, etc.
You need to be in a one of the hangars where the most consumer traffic is and where your product is among aircraft minded products and services. Or if you have an airplane that can be a part of your booth to promote your airport then you should consider an outdoor exhibit in the main area where consumer traffic is thick as well(and be out in the fresh air and sunshine). Make sure you have some shelter set up here.
Another thought if your budget is tight is to discuss the possibility of sharing space(therefore sharing costs) with another Minnesota based company, especially one that is synergistically aligned with yours or is located close to you. Look at the list of this years exhibitors to see who is Minnesota based or ask the EAA booths rep you speak to.
Good luck! And if you do exhibit I hope you will find it a good decision and rewarding.