This place is pretty Dam amazing. What a sight to see!
We opted to park at the lot close to the Visitor's Center which was $10. We then took the elevator downstairs to purchase tickets for the tour. We had my friends baby with us so we couldn't do the Dam Tour, but we could do the Power Plant Tour. It was $15 per adult for about an hour. First you watch a 10 minute film, and then you actually get to go down and see some of the powerplant itself. It's all really cool. Make sure to pay attention to the tour guide!
After viewing the plant, you get to go upstairs to the observation area and that is where you can see the Dam, Lake Mead and the Colorado river. This is the spot to take some *AMAZING* pictures. After that the tour is pretty much over and you can check out the Visitor's Center and walk across the bridge and explore. One thing to note, if you do any of the tours you have to take like 6 elevator rides. Each elevator can hold up to like 40 people so if you are claustrophobic this probably isn't the best idea. We all felt a little sickly after riding so many elevators.
My biggest issue was with the staff. Some were sweet as pie, but a few were so rude to us, I couldn't believe it. I won't go into details, but my friends and I left with a bad taste in our mouths by how we were treated. The tour guides were awesome though and friendly, so I dont have anything bad to say about that. I would say expect to spend at least half a day there including drive time. If you haven't been here yet do yourself a favor and check it out. It was definitely worth the 40 minute drive.