Can someone guide me in acquiring and configuring a wireless router for an event?

I apologize if this is the wrong subreddit.

I’m launching a new mobile app and plan to have a launch event at an outdoor festival. The festival site has good service with Verizon and AT&T, but a sizable chunk of my target users have discount carriers without service at the site. What I want to do is share enough of a WiFi connection to allow people to download the app and try it out, as well as the normal things people do when they have an internet connection for the first time in a day.

Here’s my vision: public/open SSID, with a login page that forces them to download the app (or at least view the web page) before granting them access to the internet. Then they get a certain amount of bandwidth for a limited period of time. I see setups like this in places like airports all the time so I know it can be done, but I don’t know whether it can be done on a limited budget. Also, I need this router to have as much range as reasonably possible without running wires to multiple APs.

The other issue is acquiring the actual backbone connection. I haven’t figured that out yet. Verizon’s standard “unlimited” hotspot plans are definitely a no-go since they are all limited to 15 gigs per device and I expect that amount to run out in just an hour or two if the booth is popular. However I’m concerned that I may not be able to find a plan to just buy 100 gigabytes or so without committing to a very expensive ongoing plan. But I figure I need to evaluate the feasibility of the whole plan before getting into this detail.