I used speedy cables maybe 15yrs ago for my 110. Overhaul and recalibrate, took ages to come back but looked like new, still great now.
I sent it off to this place and got it back in a week. £140 including the collection and Royal Mail insurance/postage I paid. Being it is off the road we jacked the back wheels up and went through the gears and speedo worked.I suppose costs vary depending on the amount of work needs doing.
http://www.jdo1.com is one I have found. It says fixed price repairs.