These are the sites I ordered my stuff from, although there are a kajillion places to get it.
VG (vegetable glycerin) with nicotine 36 mg/mL: $21.99/240mL or $0.09/mL
Propylene Glycol (plain): 8.95/240 mL or $0.037/mL
Various flavorings, the ones that I use often are 30 mL bottles, but smaller ones are more expensive per mL: $6/30mL (average, range is $5-7) or $0.20/mL
A typical batch for me (12 mg/mL) of, say 10 mL is:
3.3 mL VG/nicotine: $0.30
4.7 mL PG: $0.17
2 mL flavoring (average): $0.40
for a total cost of 8.7 cents per mL of juice.
I also buy cartomizers, the ones I buy are under $8 for 5, and I’ll get several days to a week out of one. I wash them, and most of the time they are reusable again. You just fill them with juice and go, the atomizer’s built in.
This, of course, is bare minimum. I’m a sucker for gadgets and tinkering, so I have to really control myself there.