Buy some larger diameter discs from the car spares place obviously with same hole spacing and dish and get you local machine shop to turn them down. That should be a lot cheaper
Always assuming that you can find the right discs and the right machine shop that doesn't have a standard half-day setup fee regardless of the number of operations to be done.
Easiest is to just do the decent thing and buy a pair of discs from your local Morgan aftermarket specialist and support small business.
After all £70 for a pair of discs every 20 years or so is hardly going to break the bank, is it?
