The variable that dominates everything above, and it is free: how you treat them.
The things that actually end boots early, in order:
Wearing the same pair every day. Leather needs to dry out between wears. Alternating two pairs makes both last far more than twice as long, which is the single most cost-effective thing in this thread and the one nobody does.
Drying them by a radiator. Heat cracks leather permanently. Away from heat, stuffed with paper, is the whole method.
Never conditioning them. A few minutes every couple of months keeps the leather from drying and cracking at the flex point, which is the failure that ends a resoleable boot for good.
Walking on worn heels. Heel tips are cheap and replacing them early prevents wear reaching the structure. Waiting until the heel is destroyed turns a small job into a large one.
Not using a shoe horn, which slowly destroys the heel counter.
Do those with a mid-priced welted pair and you will beat both the expensive-and-neglected and the cheap-and-replaced strategies comfortably.
And on your three pairs in five years: check whether they wore through the sole or failed somewhere else. If the uppers were still fine, resoleable is the right answer for you. If they were tired everywhere, the issue is rotation and care, and a more expensive pair would have gone the same way.