Just pulling your leg
Best place is
www.myprotein.co.uk
type w*w.sports-nutrition.net (obviously replace the * with a w) into the pricematcher and you'll get 10lb of whey delivered for £23
Type MP5500 code in on the order form for a further 5% off
That's 4.5kg of the highest quality whey protein deliverd to your door for under £22!

Then goto Tesco or whatever and get yourself some Oats and some cocoa powder, cheap as chips. Oats are about £0.37 for 1 kg for the value stuff or there's the much nicer organic oats @ £1.20 for 750g.
Perfect for mixing in a blender/ smoothie maker with milk for a very nutritious weight gainer drink. Far superior and far cheaper than anything you'll buy in the shops. Can also add some peanut butter for some good quality fats and a further boost to calories. Full fat milk and extra virgin olive oil are also good additions.
If you're one of those people who's fussy and gags on anything that's not as sweet as Coca-Cola then you might want to add a sweetener to it.