I bought a 5L bottle, still have half left, also fill a litre spay bottle each time I need to, I think it cost about £12-£13, it's not water based so dry cloths needed.
I was well impressed with it. First job was to remove Mazda stickers from a cars how room, I charged £60.
I used about 3/4 of a litre doing it and I soaked it. 20 mins came back and rubbed it all off.