Your initial costs will be relatively high, but still lower than smoking. There's an "experimentation phase", where you'll be trying different models, voltages, juices, etc. Plus there's the 'kid in a candy store' thing; you'll see all kinds of new stuff coming out that you just *have* to get & try.
After a while, though, you'll find your sweet spot. Everyone has one, and you'll find it eventually. Once you're there, your experimentation purchases will drop & you'll just be getting standard supplies.
Mine is a home-built 3.7v box mod with a 2-ohm cartomizer & DIY juice (spearmint is my all-day flavor) at around 20mg, 10-20% VG.
I get 100mg nicotine base in 500ml bottles for $170; one will make 2.5 liters of my juice, and at 3-4ml per day, that's 2 years worth. It's kept in the freezer & I split it with a fellow vaper, so once a year, we go "halfsies" on a bottle. Annual= $85
Flavoring & base liquids (PG & VG) are relatively cheap. Figure another $75 or so annually.
Madvapes sells LR cartomizers at lower prices in high volume (I'm sure other sites do too.) In bulk, they're $1.29 each, and one lasts me about 5 days before the flavor & vapor production become unacceptable.
Let's say I use 80 per year. Annual= $103.20
Batteries & chargers I get WAAAAY cheap from DX; they come on the slow boat direct from China, but I'm always back-stocked, so no worries. I'll give it $100 a year for those plus parts for new box mods & sundries.
Add in another $150 a year for new toys (hey, you never REALLY get all the way out of that 'experimentation phase', lol) and as a 'fudge factor'.
I estimate my total annual expenditures at $513.12. That makes a weekly total of $9.87. I used to send about $50 a week up in smoke (now it would be $60 here). So, I can guess that you'll be spending probably as much as you do now at first, but quickly your savings will start to be apparent; by the end of your first year, expect to be spending in the neighborhood of $10 a week.