Similar, smaller device is the Mifi. Portable wifi hotspot using the cell network. Dataplans tend to run a little higher than phone/iPad-based plans, but you can use one Mifi with multiple devices, provided those devices are within about 30 feet of each other. A portable wifi router is probably cheaper if you're going to use it with multiple devices, and if those devices are going to travel in proximity to one another. But if you can get by with one device, the iPad's plan remains pretty competitive, and if you have two iPad's, I think it may still be cheaper in many cases to subscribe to two iPad plans than to have one portable router.
Also keep in mind that I don't think any portable router also functions as a GPS. You can get a general location fix using wifi, but I don't know how/if that works when your wifi signal is from a portable router, and it seems like it would definitely require a data plan if it did work. If GPS is important, the 3G is still the way to go. I seem to remember that, for the iPhone at least, there was a program that would download the relevant maps to your phone so that you would have them even if you were in a poor/no AT&T reception area. If that or something similar works on the iPad, you could still make use of the GPS without paying for data as long as you planned ahead and made sure the maps you needed were already on your iPad.