A key question is how many "metal detectorists" there are in Wales searching for archaeological collectables. Roger Bland (2010, recently estimated that in England and Wales (pop. ) there were 8500 "metal detectorists" in England and Wales ( "The Development and Future of the Treasure Act and Portable Antiquities Scheme" pp63-85 of Stone and Thomas (eds.) "Metal Detecting and Archaeology", Boydell and Brewer page 71). That's one in 6406 of the population of the two countries. Statistically therefore there should be something in the region of just 470 "metal detectorists in Wales" (pop. 3006000), just 0.016 of the population.
The actual number might be a little higher, the PAS says (2007 Annual report) that Welsh metal detecting clubs have some 555+members, but some people might be members of more than one club (and obviously some "detectorists" may not be members of any clubs at all).
The discussion forum "Detecting Wales" has over a thousand members, though not all of them live or even search sites in Wales (some seem to be based in the USA).
It seems therefore not unlikely that there are about 500 metal detector users active in Wales.
Vignette: there are not as many "metal detectorists" as sheep in Wales.