That was a real billy bargain, I would expect to pay £10 or so.
Easy to do yourself, just make sure you take the stock off first, before drilling.
Cotswold cOuntry Living in Cirencester £10.00 September 2011. I watched the shop fit them to my mates Ultra. I cringed he removed stock and drilled it free hand; no measuring. He used 4.5mm drill bit then countersunk it with an 8mm drill bit; when we got home I noticed he hadn't even screwed it in properly; thread was still showing; barney bodger I won't take my rifles there.