if you are wanting to buy sand, then go for play sand £2.50 from argos/tesco/woolworths.. or get some from the lfs, pretty much the same stuff tho i would think, if you are looking for delivery, then go to tesco as they do next day for a fiver, also go to the garden centres (dobbiesetc) and you can get large bags of aquarium safe rocks and stones for about a fiver, i just got a couple of bags of blue slate chippings that can be used to make caves too.( all the stones that are safe to use in with your fish ( at dobbies anyway ) are marked as safe for fish...
but i think you are probably talikng a lot of money to have 15-25KG bags of sand deliveered from online aquarium shops, tesco are def cheaper
shelagh xxx
ps i was rambling, i dont actually know what they prefer.. how about going for a mix??
also forgot to say that play sand needs an heck of a lot of rinsing before use, but it will be well worth it. do it a small amount at the time, in abucket and do for a bout 10 mins a go