FMurtz wrote

Probably different costs to here in Australia, but what would the cheapest
stuff to use for concrete aggregate for non important garden shed floor?
In grandfathers day they used to use some sort of ash (fly ash?)or was it
crushed slag/

Not sure you can get that anymore.

You sure you want to mix it by hand instead of getting a minimix truck load
?

And in some ways you need a decent strength concrete
for a shed floor so you get a decent long lived surface
unless you want to put old carpet on it like some do.