Some battery packs may just need some balancing to restore the initial performance.
Your battery's BMS can be replaced with a new one in case it's damaged, or you want an upgrade, for instance - SMART BMS. This procedure always includes pack balancing in first place. Price may vary on a battery pack size and complexity and does not include the cost of the BMS plate.
Some battery packs may have insulation damages, this should be fixed with a new heat shrink and adhesive.
Price includes the old cell(s) extraction (and preparation for spot welding if needed) and replacement with the new one(s) as well as the cost of materials, however it does not include the cost of the Li-Ion cell(s).