I've been buying some mods, and just re-stocked nic juice, so this month was close to $400.
At this point, I have 11 good devices, and about 2 years of nic juice. The only thing I'll require for a very long time is flavoring, VG, and PG, none of which cost much. I don't stock PG/VG because I'm worried about it going bad, and it's easy to get anyway.
As far as cleartos and tanks go, I have enough to go for about 2 years, although the last six months of that I'd be limping.
So unless something catches my eye, I'm good for 18 months at minimum!
Edit: If I were on analogs, 2 1/2 packs a day, I would have spent $600 this month. So even with the overboard mods, I'm still ahead just for January!