Shops will have varying rates depending on what they do to the trans, local market going rates for an overhaul as well as cost to R/R the unit to and from the vehicle.
That said, for that amount of money, I’d want to know exactly what they are doing/installing upon overhaul. It should include the following, in addition to stuff like filter, gaskets, seals, orings, sealing rings:
1. New frictions and steels - tell them you want Borg Warner or Raybestos high energy clutches and a new steel module for all clutch packs (consider a kolene pressure plate and steels for the 4-5-6 clutch pack)
2. New TEHCM, Internal Mode Switch, wiring harness and speed sensors - all must be OEM and Fast adaptive relearn performed
3. Sonnax Zip kit installed (has updated valves for the valve body and pump)
4. Pump completely overhauled (both working surfaces machined flat/true, pump rotor and slide-to-deck clearance set at .0015”)
5. 3-5-R drum re-welded at the base where it leaks to prevent recurrence
6. Sonnax 1-2-3-4 billet aluminum apply piston installed in place of factory piston
7. All brand new bonded steel and rubber pistons/piston dams
8. New OEM rear sprag clutch
9. New snap ring for the sprag assembly
10. New torque converter with .050” or thicker converter clutch - DO NOT let them give you an oem converter with the same POS .020” thick clutch as it fails repeatedly
11. Optional unless high peformance or heavy duty: Sonnax billet 4-5-6 clutch hub with Sonnax apply/dam piston kit to run an additional friction and steel in the 4-5-6 clutch pack. The OEM hub can snap in half under power
12. Cooler bypass delete kit or at least a lower temp thermostat so it runs cooler than stock
13. New, updated parking rod assembly (these were prone to failure and if that happens you lose the ability to put the vehicle into park)