I've only ever had my wheels powder coated locally, so can't give any indication on price for diamond cutting, although I've paid around £250 for powder coating a set of 20" rims.
One location I know of in Tyrone is 'Mje Wheel Repair', based in Cookstown. I have never used them, but have heard good things about them, with one of the local detailers here in Derry/Londonderry sending them wheels for cars he details.
Their website is here:
https://mjewheelrepair.co.uk/
and if you use Facebook, they can be found here:
https://www.facebook.com/mjewheelrepair
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts
My DIY jobs -
Replaced alarm horn,
Replaced Coolant Temp sensor,
Updated RNS-D firmware,
Installed Reversing Camera and Digital TV,
Dashcam Installation,
Retrofitted Rear Blinds,
Auto-Dimming Rear View Mirror,
Chrome Boot Struts
Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights
My DIY jobs -
Fan Jet Windscreen Washers,
Retrofitted Electric Side Blinds