Hm, I haven't thought about this in a while.
So, I buy nic from wizard labs for $30/250 ml of 100 mg/ml. I make
juice at 12 mg/ml, 200 ml at a time. So for 24 ml of nicotine, that's $2.88 per 200 ml juice. The price for pg, VG, and flavors is really negligible, say $2, and that's probably an overestimate. So, about $5 for 200 ml juice, that will last me at least a month (that would be at about 6 ml vaped a day, which is more than I actually vape, so this is an overestimate). So that's about $0.16/ day for juice, or $0.80/week. Did I do that right. Seems very cheap!
I buy cartos from surevapes and punch them myself for my tanks. I get the 50 or 25 mix and match deals. 25 cartos costs me about $25, but hit up the sales when i can, so sometimes a bit cheaper. I use about 2 cartos a week (many people get longer out of theirs, but I like them fresh). So that's $2/ week for cartos.
$2 for cartos and about $1 for juice, puts me at $3 per week.
Then, I occasionally buy something new to try. About two months ago I bought a kanger protank for about $17 at a B&M store, and some juice for about $12. Then I bought a juice sampler from the vapor room for about $25 just because I was in the mood to try some new flavors. Those types of purchases are really rare for me. I'd say I'd been about 6-8 months without buying anything other than nic and cartomizers before those two purchases.