Solutions of hundreds of dollars? For what exactly?
Reminds me of the movie Hackers where they used buzzers. And why not? The only thing you gotta do is use pre-planned keywords/acronyms.
I went to several (music) festivals, big ones between 2002 till 2004 with a few smaller gigs later until 2009 or so. Back then we just used SMS or phone call. I didn't even always have a plan during the mentioned years. Especially outside the country (and NL is small) it was always a surprise to get the next phone bill (one time I paid something like 30 EUR per megabyte, in Serbia). Within the EU, these work with your normal plan nowadays.
I don't know how it is nowadays, but back then on large festivals providers would put up extra (mobile) GSM antennas at the location. I assume they still do that. I can imagine there's a lot of smartphones up in the air to record the magical moment (and ruin it for the people behind you). That alone is a reason why I wouldn't wanna go.
A dumbphone seems still clever if you go outside the country. A rugged one goes for say 30-50 EUR or so. It won't contain or give access to your whole life if it gets confiscated, no social media means you can focus on your stay, and you can still contact authorities or friends if required. Just make sure you add the personal information of those you need to contact (should be on your SIM, though possibly that's too much info as well). Oh, and the screen won't break or get damaged (if it does /care), and who cares if your dumbphone gets stolen. I suppose people generally take the risk, but I got burned once (got a digital camera as birthday present worth ~300 EUR in 2004 and it got stolen after I had it for less than a week). You can always give it away or sell it afterwards (like a real burner) or reuse it for the next journey.
Now, back when I went to music festivals, you'd sortof stay together cause you could find each other but it was a bit annoying. If you could automate it, like you can give your position with WhatsApp, then that'd be great. However, with WhatsApp you decide who can access your location, while with this solution its available to all. That might not be what you want.
Other sports like hiking, skiing I can imagine to use this technology. Even people who live "In The Wild" could meet up with other total strangers, if that's your thing. I mean imagine using this in some huge forest in Canada, or on Greenland where you suddenly notice another life form.