They decided to go and look at the local computer shop who do a lot of refurbished PCs. I went with them today and we managed to get a small form factor Dell Dimension (similar to the current one), with a Pentium Dual Core, 4GB RAM, and Windows 10 for about £140.

Should be decent enough for what the bloke needs it for and should be an improvement on his current Sempron/1GB/Vista system.