Sorry you had an accident.I hope everyone is okay.
This is hard to estimate due to not being able to see the damage. Also, are you talking about the body work or just fixing the light or both.
If the light does not work, I would remove and check the bulbs. Many times a hard hit like that brakes the filament. So test with a good bulb.
Also if the tail lamp assembly is broken you can pick one up for about $62 with shipping from the GM website. Do you want that?
Next, a salvage yard many times you can locate parts at a reduced price and they are just fine.
You best bet on the damage is to go to several body shops and ask for an estimate. At least 3 to 4 different locations. Depending on the damage, they may be able to knock it out or have to replace the entire panel.
Please get back with us if you have some concerns.I hope this helps. If not, please let me know.