Arcade style games that have a time limit would be good. Having people play against each other would be fun. I know playstation has some games for up to 4 people.
Pulling out the older games like Packman would get the parents to play. Set it up where there's enough room to watch. You could keep a white board listing the best scores to encourage players to come back.
Offer a prize for the top scores of the day or hour.
As for what to charge, well, Chuck e Cheese charges 25 cents for a game but I've seen places in the mall that charge $1.50+ per play. You can charge more money if there's a prize at the end. See if you can get a gameboy or things like that donated.
I set up a Playstation with Dance Dance Revolution at a carnival and it was a big hit. We used one of the school's TVs on a rolling cart and hooked up our own Playstation and the dance mat. We charged one ticket to play. I had my son helping with the game for most of the evening in case anyone had problems. This game worked well since it had a definate start and end. Other games that might work would be racing-type games that don't take long to run one race.
