I would not pay 250 for a used mk2/s600. The first stage is the more important one and there is a lot of difference between mk2 and mk25. I paid $175 for a brand NEW mk2/r295 last year at an lds that's an authorized scubapro dealer.
Look up prices for a new mk2/s600 and then divide by two and you'll have a reasonable expectation for a used reg.
Look up prices for a new mk2/s600 and then divide by two and you'll have a reasonable expectation for a used reg.