I use Charlie Chinchilla Sand and SuperPet small animals litter balls currently. I spoke a bit about potties/sand baths recently in this Section - check it out here:
Does your hamster drive you potty?
I personally think children's play sand is too gritty/large and coarse to really get into the coat of Long-haired hamsters, and my large container of Charlie Chinchilla Sand lasts for ages, definitely less than £1 per week - and I have a lot of hamsters, and baths to fill