vernier

hey there, 1997 corby sx 1.6 with kent cams. After trying everything cars still runnin a bit lumpy and the fuel consumption is getting a bit silly at times. Been to the garage today and been told i need a vernier pulley for my kent cams as they need adjusting. the garage want £148 quid...

as title says,who does them for the abf and what what sort of price am i looking at? cheers mat