I can usually get 15 ml for about $8 depending on the quality. And then online you can get all kinds of deals. I like Mister E Liquid (
http://www.mister-e-liquid.com) but there are a bunch of links in this thread to juice suppliers. I have almost always found it cheaper online. I have been mixing it together though since I found out that you can vape the VG that you buy at a drug store. Just make sure it is USP grade. I ordered some stuff online that I knew had really good strong flavor, and I ordered it 100% PG, it was $14.50 for 30 ml. Then I bought some VG from Wal Mart. It was something like $3.50 for a 177 ml bottle of the VG. I mixed it about 80/20 (vg from Wal Mart/pg from juice) because my atomizer works pretty well at high VG levels. That gave me 150 ml of juice for about $17. I have a few little bottles of local store bought stuff that I mix in with VG as well.