ScubaPro Mk2+ with R190 2nd stage. Decades old design, near indestructible, and a good performer. It's okay in cooler waters too. This is ScubaPro's "cheapest" regulator package, but hey it's friggin' ScubaPro. This design is extraordinarily easy to work on and get parts for.
For a bit more, swap to the slightly smaller R380 second stage. It's the same mechanism as the R190, but in a 25% more compact housing. Slightly less durable.
I've used this rig for years in Texas and the Caribbean, with little/no maintenance and rough working conditions. I keep waiting for it to break so I can upgrade, but it sadly disappoints.