USA3000 services PIT. Yes, they are primarily used as charters, but seats can still be booked against on their website or via phone.
I've flown them once, PIT-MCO-PIT
It was fine. Clean planes, polite staff, and snack service. At least out of PIT, their schedule is limited to particular days of the week. For example, outbound to MCO might only be on Sundays, Tuesdays, and Thursdays and return on Saturdays, Mondays, and Wednesdays. So, you might have to be able to bend your schedule a bit.
I'd fly 'em again.