The arithmetic can work and it depends on one thing people rarely check: construction, not price.
A resoleable boot has the upper attached to the sole in a way that can be undone and redone, typically a welted construction, where a strip is stitched to the upper and the sole is stitched to that. A repairer can cut the stitching, replace the sole, and stitch a new one on, several times.
A cemented boot has the sole glued directly to the upper. Some can be re-glued once, badly. Most cannot be repaired at all.
Price does not tell you which you have. There are expensive glued boots and mid-priced welted ones. So the question to ask before buying is what construction it is, and a seller who cannot answer is telling you something.
On the numbers: a welted boot typically costs several times a mid-market pair, and a resole costs somewhere around a third to a half of a cheap pair. Two or three resoles over a decade or more, versus buying five or six pairs in the same period, does come out ahead: but not dramatically, and only if you actually do the resoles.
The honest summary: it is roughly a wash on money and a clear win on having one pair that fits and improves.