A proper refurb won’t just be a dip-strip-coat job.
It should also include proper repairs to any rim damage (stop sniggering at the back) and checking for round/true.
£300 for a full set of four is £75 per wheel which sounds pretty good to me but just make sure about what you’re getting for your money. Ask the provider if he can show you examples of his work.
As far as decent aftermarket wheels go, depending upon the size of wheel you go for your probably looking at the thick end of £1200 for a full set plus tyres, if not a lot more. Team Dynamics, O-Z, Kahns, Borbets and the like do not come cheap.