I make about $5/month on Food Trucks Near Me [1] through ads. At least it's not losing money!
I would try something like $25 a spot and try to make them sign a 3-month advertising contract. If they balk, just remember you have 30 other food trucks and only 3 spots. This makes more sense if you had a good amount of traffic.
I am considering a lower pricing tier for a menu. Currently only St. Louis has a couple menus, because curating and formatting the menus is a pain.
I've been working on a cached serverside implementation that uses multiple IPs to overcome this, but it's too much of a pain. In addition, I would have to completely redo the UI to accommodate that many trucks.
I think that the current site will stay for mid-sized cities (30-50 trucks) unless a developer steps in. I had almost finalized giving 49% of the company to have the rails shop in town completely redo the site and do the caching.
Also, to reiterate what other people in this thread have said, find better ways to monetize this. Think about bigger ads, charging trucks to send email to your subscribers, etc. Traffic solves one of the bigger risks for a food truck.
Having a real business plan here means you can give away a much smaller chunk of the company, or pay cash, and give away no equity.