I think around £1000 Be sure you get a safety mechanism installed too, if there is a fire the ramp electrics fail and it's stuck up.. Try trucksmart in Devon.
We have a valve on ours we are supposed to press if this happens, but the ramp then will be down until the whole thing is fixed again...
Is pretty much the same for sprung and hydraulic. Personally I think Hydraulic is a pain in the Ar*e
Minw has a lever to release the hydraulics to lower ramp anyway. Is only hydraulic on the way up. It really is just another thing to break tho (mine is broken at the mo!)