What is the average income / cost of living of UK couples now?

I'v asked this question by my friend who wants to come over to UK to live with her boyfriend. Although, she is very concerned about inflation,high cost of living, and job hunting. I want to help her providing some information, but have no idea about it.....Can someone tell me approximiate income/cost of living of couples in UK now? Or if you could give me some websites which tell about it (With not too many jargons, please!), I will be very grateful. Thank you.