If you go through AT&T, you'll likely have to get the crazy data plan. Get one from an Apple store in your city, or from the Apple store online. Since you can't really unlock the 1.1.3 phone (and you should have no need to), you should be fine.
I did a little checking, and here's something you might be interested in -
iPhone users can now drop data plan, save $20 per month - Engadget