I like to mix sand, sphagnum peat, and topdress with long fibered sphagnum (LFS). All of those can be purchased at something like Lowes. Unfortunately, if you are only talking about a small amount of need, this is overkill. So if you only have to fill a small amount, I would simply buy a bag of LFS, for ~$4-5. Rinse all media, especially sand and peat if you use it. Pool filter sand is also very good. Sand from the Building Materials section is good, as well as sand blasting sand. The big bales (2.2 or 3.5 cm)of peat are the correct peat to use, not the Scotts brand, with all the ferilizers.

A 50/50 mix of perlite and peat moss.