1. I'm pretty sure the cost to go up the Arch is 10 bucks for adults
2. There should be plenty of parking near the arch
3. Forest Park (The 2nd largest city park in the country) has a very nice and free zoo, there's a great art museum (if you are into sissy stuff), the Anheuser-Busch brewery tour, aka free beer, and I'm pretty sure the Baseball Hall of Fame's travelling exhibit is now at the history museum there as well, also, there are plenty of good bars all over.