An indication of where you are located in the US would be useful. I will however be frank, 999 out of every 1000 keys are most likely worth nothing more than scrap value. When you have such a huge number even looking them over it likely to take a lot of time and effort, so you either try and sell the whole lot to one collector (hard - very few collectors would want such a qty) or try and compensate someone knowledgeable for their time in checking them out.
In the former case I would guess that you would only get a small premium on the price of scrap metal. If you opt to have them checked it will probably cost you some $$ to do so but if you have anything good or rare it’s the best chance of it being recognized.
I would advise against talking to a regular antique dealer etc, this is a highly specialized field and in my experience general dealers or auction houses know nothing about it.