To be honest the clay was used up anyway - I'd only used half a bar for the whole car and it had a lot of grit in it, I doubt I would have used it again.
Buying individual bars of Sonus of the web is about £6, whereas the Megs kit for example is loads more.
I was reading on detailingworld.co.uk that some pro detailers mix water into their detailer to make it go further, while still giving a good lube, so if your trying to save a few quid like me I guess you could do that.