I remember robbing a store with 3 other people. I didn't see exactly how much I bagged at the time, but when I split the cash as we were escaping @ 25% each we definitely each got over a grand. There are big ones out there for sure, I just hope it scales a bit as you level.
And yet I did. Got $7k last night as well. There are definitely jackpot stores out there.
10K is a lot of money for doing a decent co-op mission, you won't have pulled that from a convenience store robbery.
I've definitely pulled $10k out of a store robbery before