How far it has gone, and the three thresholds
Open joints with brick in good condition is repointing. Brick faces spalling and courses moving is partial rebuilding, commonly from the roofline up where exposure is worst. Movement below the roofline, or a stack out of plumb, is a different conversation involving the structure below. Those three thresholds are visible from a proper survey and they are the largest single determinant of the number. A proposal that does not say which of the three it is has not established the scope.
Access, which people forget entirely
The same repointing on the same square footage costs differently on a single-storey ell and on a tall stack over a steep pitch, because one is a ladder and the other is staging. Access is a legitimate and substantial cost and it is not padding. What it does mean is that grouping work, doing the crown, the cap, the flashing and the repointing on one visit, is materially cheaper than doing them across four visits with the same access set up each time.
Cause versus symptom
Nearly all masonry deterioration on Vermont chimneys is water plus freeze-thaw. If the crown is cracked, the cap missing, or the flashing failed, the masonry will keep taking water after you repair it and the repair will fail on the same schedule as the original. A proposal that repoints without addressing the crown and cap is quoting a symptom, so the sequence on our waterproofing page is crown, cap, flashing, joints, and then treatment.
Season, and why a cheap winter quote is not a saving
Mortar needs temperature to cure. Vermont's window for exterior masonry closes earlier than people plan for. Work carried out in marginal conditions can look finished and never develop strength, failing in a way that is hard to attribute later. If the only availability is late in the season, ask directly what the conditions requirement is and what happens if the weather does not hold. Deferring to spring is frequently the cheaper decision.