There have been a million discussions on this over the last year or so along with various tests done by Buzzards with too much time on their hands. If you do a search I'm sure you can find them, but I'll sum up my take on it since I'm also in the market for a cooler and I've read all the threads.
Yes, the really expensive ones might work a little bit better, but not enough for the money. The most important thing is cooler management (keep the lid closed, cover with wet burlap, etc.).
I think I've decided to go with this one:
102 Qt Gottâ„¢ Marine Cooler | Ice Chest | Rubbermaid
It's a better price and a buddy of mine used it on an 8 day Deso trip in July and we still had cocktail ice on the last morning.
I also really like the freezable dividers. My .02