Welcome and glad you joined.My question is how long should these coils last?
Not long, sounds like you may motivated to start building and wicking your own coils. You could do this in stages, like buy a premade wire coil and wicking it yourself. Could read:
How to get the most from your vape coils
Selecting a Tank | Sublime Vapor
You Tube is a good source in learning hand eye techniques regarding coil and wicking.
The rebuildable information below may help you:
(7) Information Resources for Your First RBA | E-Cigarette Forum
Wrapping Building Coils 101 For Beginners
Rebuildable Tanks Explained: RBAs vs RDAs vs RTAs vs RDTAs
Rayon Wick - Better Flow, Flavor, Longevity, and Nic Hit!! - Pt.2
Rayon wick, better flow, flavor, saturation and Nic Hit!
Could ask detail questions here: Wick and Wire