I'm not a machinist/turner but a faceplate can be used to hold the NSR head on a lathe.
I think that would keep the cost of machining down at a machine shop.
Of course, if a jig has to be made. Then you would expect to pay more.
You would of course be paying for the time it takes to set up the head on the faceplate also.

It was £50 per head at Derek Huxleys' for what I had done. I think that's quite reasonable. He didn't charge extra for the damaged head, although it must have been at least slightly more work.

We'll have to find out what he charges to repair Pauls' damaged head.

I don't know what a new head would cost but I'd bet it will be more than the repair cost.

Just checked. £151.13 plus VAT for a MC21 rear head. Stocks are very low and it may take 3 weeks to arrive.