You can buy stepping stone moulds off Ebay and make your own for less.
I have a couple and have made stepping stones for just about everybody I know (and a few I dont)
You just buy the mould, mix up some cement, sand, fine gravel (ie =concrete), add some colour (a tin from Wicks), pour it in, let it set and tip it out.
Moulds cost anything from a couple of squids for a small one (say 9"x9") upwards. My big log one, 18" dia, cost a fiver, and has made about 40 stones so far. (£5-£10 each in the GC.)