I honestly have no idea how much I vape in a week, or even a day. I drip and always have more than one flavor going, so I have to take a wild guess. I'd say I go through 1-3ml a day, so probably about 10-20ml a week, which works out to (averaging the cost of all the brands of juice I use) about $9-13 for a week. Add in the maybe $0.10 for wire and cotton when I have to rebuild, and I'm still under $15. When I stopped smoking, I was paying about $25 a week for cigarettes.
I'm pretty sure at this point that I've broken even and started to save money, but it took over a year and a half for that because I was experimenting with toppers, buying new devices, etc. At my last count, I should I have broken even by August 2014, but then I bought some stuff, so I'm guessing I've probably saved about $300-$500, finally.
The point of all that being that vaping was definitely more expensive up front, but now that I've found devices, toppers, and e-liquids I love, I'm probably saving some money, and will continue to do so.