Project update:
I picked up a few Axis C8033 devices. They are only a couple hundred each. Aside from firmware being WAY out of date on them (one came with 1.9 and the other 1.8, with the current version being 10.x) after updating, configuration on a local network is dead simple. Set up one as a 'leader' and the others show up and get connected.
Out of the box, it was set with an audio buffer that had 120ms delay. I found in the advanced settings where I could drop that to 0, and now there's almost no perceptible latency at all. Impressive!
Next step, to make things wireless, I attached them to a pair of Ubiquity isostations, which I've used in the past for wireless hops of about this length, and so far, everything is working as expected.
I should be able to stick them up on tripods for the event and call it a day.
But, then, here's where the fun comes in. I was able to also configure them as SIP devices and tie them into my phone system. Latency of the phone system is roughly 100ms, which is totally acceptable for this sort of distance. Now, if I can find an internet connection, I can connect to the broadcast. Very very cool little devices.