EllinK,
For our first trip (Greece), my husband had just gotten back from Deployment, we had a big chunk of money and were feeling very Carpe Diem! We decided to splurge. As it ends up, we found ABD prices close to the vacations we usually take when all is said and done (it's still more expensive by a bit but not as much as I thought).
ABD is a big expenditure out of pocket but we end up spending very little money on the trip (in Greece, we spent like $500!). We are not big shoppers but so much is taken care of, we end up not spending too much.
When we cruise, we go nuts! After the spa, the cabana, and souvenirs, we are in the same ABD ball park. Because I am insane planner (financial and scheduling), I think that ABD gets expenses out of the way and we can just enjoy the vacation without me mentally tabulating every expense and updating my spreadsheet on the cruise ship!
Again, we don't do many pre-days and we are banning post-days (we miss the group and are usually ready to get home) so we don't incur too many expenses there and on the trip, I found that the plans I made for on your own time (Theatre in London (eveyone fell asleep, except me!), Dining Reservations--we are huge foodies) often did not work for us because we were tired from the group activities or found we just wanted to chill out at the Hotel Bar or just relax in the room. That helps control expenses, too.
The Arizona/Utah trip is wonderful! We had a wonderful group on that trip and two great guides (Hanneke and Kim). I would encourage you just to make the leap!