Hayley slim fast shakes are much higher in carbs when I tried that cheap option I was always hungry and ended up giving up and going back to normal food. I doubt they keep you in ketosis.
If you really can't afford CWP I would try Slim n Save.
Have you tried the vanilla, chocolate and chocolate mint shakes? They are my favourite I have a mixture of those a week and the apple and cinnamon porridge every night