no problem Michael, I answer to Tim or Tom
Hi Mike, the GM ones are reasonably easy to find on e-bay and dealer sites, the enamelled ones are a bit harder to find though. Pricing is all over the place, but you should be able to pick up an all GM version for around £15. The enamelled ones can be tricky, as they are usually priced way too high, in my opinion; but If you're patient, you may get one around £40 or even under, but most are in the £45 - £55 range.
If you have access to a militaria fair, that may be your best and cheapest option. I will be at Stratford this year, (9th June) happy to look out for one if you want - just PM me.
Also, beware of repaired enamelled ones, where the enamel is not a consistent colour.
Cheers, Tim