Ravenheat 3 way diverter valve replacement costs

I have been ringing around for a price on a replacement 3 way valve for a ravenheat csi85. Can anyone suggest why prices vary so much?
Plumb centre £147 +vat, Ravenheat about the same
Couple of web sites £90 and down to as low as £60
I did get one which was £23.50 + vat
Is this price differential existing because of consumer ignorance or is it manipulated?
What do you think?

The expensive ones will be original parts, cheap ones will be Chinese copies

I have looked at this problem for years so i got in touch with giannani and they told me that they make them to suit ravenheat boilers, and the pressure of the springs are different to the lookalike valves, even though they look the same, i used one once. and the boiler would not cfire up with the washing machine and one of the showers . so i put on a genuine one and never had any problems after that

mick