Tuna radar buoys are dropped regularly in the sea, and are quite a bit north of $500, I believe. They are not expected to be recovered, work completely off sola

Tuna radar buoys are dropped regularly in the sea, and are quite a bit north of $500, I believe. They are not expected to be recovered, work completely off solar, and are closed solid. You need a magnet to turn them on through a reed switch, they don't even have a hole for a button to prevent water ingress.