Can't tell which side of the pond you are on. I brought just the CNC machined head advertised with this pier: link I think I paid around £80 for it. The boss you take off your existing triod.
The top and bottom plates I got cut and drilled from a slab of steel I had lying around. That cost me again around £80.
-------------------- Orion Optics UK 350mm Dob
Celestron 8SE
Bressier R-127L + minus violet filter(F=1200mm achromatic)
ETX125
Revelation 80mmED
W0 ZS66
EQ6 Pro
DSI I