Low cost swarm positioning
It's an interesting idea. You mention an esp32, and it being a widely used wifi networked device works in your favor.

I think you have a couple of challenges in the project. First is that all devices in the swarm have to be operating in a precisely synchronized manner. I've come across White Rabbit project that make use of a very precise clock synchronization protocol across multiple devices on a network. Using this type of protocol would allow the swarm devices to operate in the same time frame. With some equipment you can easily cover the area specified with a single wifi network all swarm devices have to be connected to. I haven't looked at implementing the protocol on a microcontroller, but it should work in principle.

Second challenge is generating an event, or series of events, detectable by all swarm devices in the specified area, and applying triangulation principles based on the time difference measured by each device in the swarm from the moment of event triggering. 500x500 meter distance isn't too large for an audible frequency sound to travel (single-tone whistles can be detected from kilometers away). Having a small microphone listening to the specific tone triggering an interrupt to time stamp an event is all that would need to be done. The base station setup would perform self-calibration from the triggered events to account for the effect on sound speed by temperature and pressure. To get 1m accuracy you would need to be able to detect an event with a precision of under 3 ms, which is achievable on the esp32.