First off, that fare of $670 and $430 is WAY too high. You can fly from Detroit to Phoenix round trip two times for less than $670. (no kidding) So what ever you do, as long as you book your fare now you won't have to pay anything near that cost.
Second, seriously reconsider flying. There are only two good reasons to not fly that long of a distance. 1.) Road trips can be really fun, but usually at the cost of days of travel time and the loss of being economical 2.) You have a car and you need to bring it with you (i.e. you are traveling one-way...just paying gas will obviously be much less than buying a fare) Airfare can be really cheap when booked in advance and between major airports. My round trip airfare to Europe for the World Cup last May including taxes and fees was less than $500. (and that was including the extra cost to fly into one airport and leave from a totally different airport in a different country)
Go to Orbitz and Travelocity. There seems to be something wrong with Orbitz's website right now, but Travelocity is finding fares as low as $325 round trip in June. With taxes and fees it is still less than $360. Also, I just checked Amtrak and found one way fares from Detroit to Phoenix for $230.
If you really want to travel by land and cannot drive yourself, you could try using Megabus. It is a discount bus company out of Chicago. They only go as far as St. Louis, but if you can find a super fare (they're sometimes as low as $1) you can make it all the way down to St. Louis for hardly anything and cut out some of the fare costs and then take a grey hound or amtrak from there.
Back on to the airport subject, don't let the security checks and hassles turn you away from flying. It really isn't that big of a deal; I've flown through both Detroit and Phoenix's airports many times and they really aren't that bad. Looking at the big picture; spending 30 minutes sitting in line at the security check point is much faster than sitting in a train seat for 40 straight hours. Driving would probably save you 10 hours if you drove straight through without stops, but I've done that before and it sucks.
Weigh your options thoroughly. It appears at this time that flying will most definitely be your cheapest option to get to Arizona. However, if you want to experience a good road trip or train ride, definitely go that route. Just remember that flying will not cost 3 entire days of extra travel time and won't cost extra money either. Although that long grey hound can be pretty intriguing, it is never worth paying extra for the experience. My advice is fly.
Also, Phoenix is Phoenix no matter where in the area you will be. Even if Surprise does get a little cooler at night than the surrounding area, it will still be stifling during June or August; even at night. Be prepared to get hit with a wave of hot stinky air when you get there. (nothing against Phoenix)
