Anywhere from $200-$2000. The problem with them is they corrode SO BADLY! Lower units for them are next to impossible to find used, and when you do find a good one they want $1000-1200 for it. New lowers cost almost $3500 last I heard. And the lower units are almost always junk if they are used in salt. The powerheads are good if they make it past 500 hours, but a lot of them had boron problems with the cylinder walls as they are boron coated and the boron is known to fail without any warning. And was it mentioned they corrosion problems, because they suffer from it BAD!
Overall I like them from a power house VS weight aspect, as well as being reliable, but they can be pricey if not maintained and they corrode BADLY!