I went apeshit last year and added two 104 qt coolers to my collection and shared them with a couple of people in my camp. One had 50 pounds of dry ice ($20 total from the local Airgas distributor - forget that grocery store stuff) and the other had, well, everything else.
I ate extremely well. Better than I normally do, actually. I opened no cans, boiled no noodles, and ate food that was either fresh or prepared the week before and frozen or frozen to begin with (ice cream!)
The dry ice lasted 6 days. The coolers sat on top of a camping pad, had a blanket on top (most of the time) and the dry ice cooler had another one placed inside when it started to empty out. I think that helped. They were also in 24 hour shade. They were opened only when necessary and water was drained out often.
One rule that I set up but wasn't anal enough about enforcing was the need for everything to be in a sealed container. Next year, EVERYTHING will be. Including bread, containers that don't stay sealed completely (sour cream tubs) bags that get opened and put back (folding them in half ain't good enough) and anything else I'm not completely confident about. Ziplock bags are cheap and can be cleaned and reused after the event. Once the food gets in the water or the water gets in the food, I can't use the water for a cold afternoon shower and can't dump it on the playa. Soggy bread tastes like crap. Cooler water should stay clear!
If you're flying out of town and not keeping the cooler, I'd just try to find the least expensive 50 quart cooler at the Walmart of whatever. The Coleman Extremes will save you a few bags of ice which is nice, but if it costs $10 more you probably aren't saving money if you only use them for one trip. For multiple trips or use the rest of the year, they rock.
I'm not sure how much stuff you're bringing.. one possibility might be to buy a 100 qt cooler ($50 off the shelf, less if you can find a used one) and use it as checked luggage. Strap the thing shut for the trip cause those latches and hinges aren't very secure. When you get into town, transfer the gear to bags and load it up with food and ice. Check with the airline of course.. make sure the size is within their guidelines.