My cost is about $0.086/ml for 10 mg/ml, 20% total flavoring. The breakdown is below.
I typically get my nic from goodprophets on sale, $14 for 120ml of 36 mg/ml, $0.117/ml of 36. I vape 10 mg/ml, so my nic cost is about $0.0325/ml.
My all day vape uses 20% flavoring, 10% tpa tob blend that I get from goodprophets, and 10% vanilla from natures flavors, 0.1 ml/ml of each. The tpa is $7/30ml, so $0.23/ml, or $0.023/0.1ml. The vanilla I get 8 ounces (240 ml) at a time, but their shipping is high, ends up about $47/240 ml = $0.20/ml = $0.02/0.1ml. So, total flavoring cost is about $0.05/ml. (I orund up on this one, just to capture extra shipping gludge -- it's actually slightly cheaper.)
Nic base + 20% flavorings = $0.0825/ml.
Nic base is about 0.3 ml, and flavorings are 0.2 ml, so I have about 0.5ml/ml filler. If my nic base is VG, then the filler is PG. I use a gallon of tractor supply store PG USP, $23/128 ounces = $23/3840 ml = $0.006/ml, so $0.003/0.5ml.
Grand total = $0.0825 + $0.003 = $0.0855/ml ($2.57/30ml) for high flavor (20%), 10 mg/ml, using well regarded TPA and Natures Flavors flavorings. I vape about 6 ml/day consistently, so run about $0.5/day eliquid cost.