What’s a reasonable cost to seal accessible duct joints before insulating?

I’m comparing scopes for sealing ductwork in an accessible attic or crawlspace before replacing insulation. The main question is whether targeted sealing at visible duct joints is worth paying for now, or whether it makes more sense to pursue broader testing and air-sealing work first.

For a quote, I’d want the contractor to separate:

- Duct-joint sealing, including the sealing method and number of accessible joints
- Any damaged or missing duct insulation
- Duct replacement, if a section is actually deteriorated rather than merely leaky
- Leakage testing before and after the work
- Extra charges for tight access, long runs, or contaminated areas

What cost range have others seen for this type of work? I’m less interested in a whole-house attic air-sealing estimate and more in the labor and materials for accessible duct joints.

I’d also like to know what symptoms justify professional testing. If only a couple of rooms have weak airflow or unusual temperature differences, does that point toward duct leakage or restriction in those runs? Conversely, if airflow and comfort are generally fine, is visual sealing of obvious joints usually enough to do before insulation, or is testing still worthwhile?

I’m trying to avoid paying to replace every duct when targeted sealing would address the problem, but I also don’t want to bury a significant leak under new insulation.