Why? Even 200 in a small area, say a ski resort, mountain bike race, or similar seems perfectly reasonable. Sure not 200 people typing as fast as they can, but plenty for the normal chatter I hear over sms. Especially if you keep the messages short and have a latency of a few minutes be acceptable.

Using the family radios (often $30 ish) on hiking trails, parks, amusement parks, etc. I usually hear minimal chatter, just things like "Anyone seen Bob?", "meet at lift #4", "Lunch in 30m?", "Linda stopped to retie her shoes", etc.

Check out js8call if you want to see how to handle 100s of people with very little bandwidth. Sure it's designed for ham radio frequencies and covers 1000s of miles instead of 1000s of feet, but still man portable

A phone, bluetooth sound card, a HF transceiver, and an antenna is all you need. Generally hams are proud when they get better than 1000 miles per watt.