I paid $150 to park in the South Lot. The cruise terminal area in Galveston is very safe. I strongly recommend pre-booking your parking though, unless you want to be parked out in the back 40.
Formal is whatever you want it to be. Cruise casual too. On a formal night you will see dresses, jackets, ties, polo shirts, khakis, t-shirts, jeans, and shorts. Same goes for cruise casual. It's completely up to the individual. The only thing that will keep you from being allowed in the Main Dining room is swimming attire, and tank tops for men. (Something about visible arm pits) The opportunity is there to have a professional photo taken if you wish $$$. This is the only thing that can play into your decision on what to put on. Again, that's optional and for a fee. Basically, You do you. Enjoy.