Ask what fault has been identified and which work the quoted amount covers. The grinding appliance, control accessory, sink mounting and connected waste fittings are different parts of the overall arrangement.
What the observation tells you
A figure described only as a disposer repair can be difficult to compare if one proposal includes a pipe connection and another assumes it is already sound. Confirm labour, required parts and any separate access or follow-up work before approving the scope. Do not assume a replacement component cures an unassessed drain problem.
A useful next step
Keep the written estimate and diagnosis together. If a discovery changes the proposed work, ask for the revised scope to be explained before proceeding.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.