Depending own how many slabs you want to lay,it works out much cheaper per kilo and is a lot less effort to order a big bag delivered, rather than getting lots of small carry- home bags. We get a big bag every year or son and keep the remainder covered and clean in the bag, and then we have plenty for the next job, whether mixing mortar or laying slabs on it.
But if you're only laying a few, they do take up quite a surprising amount of sand, and then it works OK not to have the sand very thick, just use it to help level off the hollows in the ground really. If you can get the earth area fairly level all over to begin with, and the slabs level with each other at the edges as they go down, they seem to settle down into place even on mainly earth. But it's quite time- consuming to do this and some of them need to be lifted and replaced several times before you can get it right. A long sprit level is a big help with this, placed across the edges of the two slabs you are trying to match up. It's a good way to do the job, though, because you have the option of changing things if you want to later on, and its less trouble than mortaring them, also allows for drainage between the slabs to some extent. It wouldn't be a good method for heavy traffic such as drives, but what I did round the chicken run has stayed level for 18 months of daily use so far.