I have done it many times, £400 seems very high, is this just for the cylinder and piston and labour to fit it? it may be for a crank shaft as well, which would mean splitting the crankcase, fitting seals etc,i would allow 2 hours on a clean machine to do a crank/cylinder and piston, 1/2 hour labour to replace the cylinder and piston only, try to get a break down of this estimate, pirate cylinders are available on E Bay for around £60, labour rates are around £30/£40 an hour.
Husqvarna man, July 2010