If you have an Autosmart dealer near you, you can pick up 5l of Smart Wheels for around £15. I dilute mine 5:1 in a foaming spray bottle and it lasts ages. I normally use normal shampoo in a bucket with the halfords alloy wheel wash mitt and associated brushes.
I got a good foam spray head on my Bilberry at the weekend. Great tip that ! Hardly used any.
Thanks for heads-up on Autosmart too