We have just picked up a used, but in excellent condition (virtually unused actually) for $300.
Screen is smallish I think- maybe 6" x 10" but crystal clear. It's an
Autohelm, which was purchased by
Raymarine. We felt that used, given the lack of moving
parts, was the best for us. Like you we were not shooting for a high speed integrated system. Used made it easier to avoid the electronic octopi, with their multiple electronic tentacles...
Had to have a missing cable fabricated but that turned out to be easy.