I pay around £2 or £3 per can, it lasts a good couple of months if the misses hasnt got her hands on it, it now lives in my boot with emergency tools and trolley jack lol.
I buy it from the local car hand wash place, depending on how many they have in, the price changes - or im sure they just make it up as they please.
Anyhow - love the stuff, remember to use it 10mins in advance as it can be strong, very good alternative to use in the house, if you have money to burn - its good for cleaning / polishing trim.