The question depends on what kind of life your living, who you are, and what you need and want. Obviously the people that have the money to spend, have the option to spend that money. The Doctors and Lawyer vapers have no problem buying a new GG and ZENs and a Caravela and maybe a Bogwa and whatever the newest most coolest $400 mod on the market is. They have no problem saying "I STRICTLY VAPE BOBAS BOUNTY!" or "I ONLY VAPE PLUID WITH MY FOUR IHYBRIDS!" or "I ONLY use blown glass trippy tips!" lol. They have no problem dropping $150 on a ZAP for their provari or $200 on this genisis or $200 on that one. That can become hundreds of dollars more expensive than smoking. They are enjoying themselves and they are spending on their new hobby.
U can be on the opposite side of the spectrum and use cig-alikes with DIY juice. Or eGos with DIY juice. Or if you can afford it, you can find a couple juices you enjoy and keep them on hand, but mainly make your own. Have a couple mods that you always saw and always wanted. Maybe buy a new mod every 2-3 months. Maybe a new RDA once a month with your juice purchase. Its all up to you.
I spent around $35-40 a month on a bag of tobacco & a box of cigarette tubes. If I don't buy a new atomizer or a new mod, and I haven't run out of a needed flavor, I can get away with buying a 20-30 dollar bottle of unflavored 18mg juice and make that last 2 months. So in juice, I get two months out of the money I used to spend for 1 month of smoking. But with vaping you do need to maintain your collection. Buy new batteries once a year for all your mods you use regularly. I just had to drop $40 on batteries. Vaping has more costs for me than smoking RYO cigarettes did. When I smoked my mom had no problem giving me $30 for a bag of tobacco because shes an ex smoker and she knows how hard it is to go without. With vaping on the other hand, my mom refuses to give me any money. In fact, if I went downstairs to ask her for $5 for juice she'd start hollering at me. If I went downstairs right now to ask her for $10 for a pack of cigarettes she'd give me $6 and tell me to buy an off brand. lol. But, vaping has 0 to nilch chance of killing me so I'm with it.