How far West are you in Wales Attila?
If you're in Carmarthenshire, it may be worth popping in to Carmarthen Cameras (I've no 'interest' in the company, but have spent some of my hard-earned with them - they supplied my grotty old black MX and a 40mm f2.8 pancake lens for £80 with a 6 month warranty - not bad I thought).
Have a look
Pentax manual Lenses | Pentax SLR Lenses | Carmarthen Camera Centre Ltd., Digital & Used Cameras & Accessories
the M135 f3.5 may not suit your needs, but at £35 it's a reasonable price for the claimed condition.