Also try Halfords primer rather than
GW.
The Vallejo 'Game' colours are based on the old range of
GW paints but should still match most of the current.
Your best bet is to go to a show, like Salute in London (although that happens every easter) and compare side-by-side to be sure.
I have aslo bought stuff from
http://www.gamingfigures.com/ and found them very good. 15% of
GW stuff.