yeh its expensive, this is from his listing
"
We are pleased to offer this excellent replacement 150cc GP Big Bore Kit
This is a 150CC GP Big Bore Kit
Its the most POWERFUL kit you can buy
Comes with a forged, single ring RACING PISTON, converted to flat top.
Also Includes your head remachined, Especially designed for the 150 Kit.
Barrel is Blue Printed, BORED and RE-PLATED.
Comes Complete with TOP END GASKET set and SMALL END BEARING.
You need to send your barrel to us for the work to be carred out"
ken