lf you want to buy one cheap, go to www.alibaba.com. Its cheap because you can buy directly from the manufacturer, no middleman involved.
I have used a 3g pocket wireless router. It takes modems through USB and personally l will not recomend it for mobile use. To start with, l was using Powertel modem and it only connects when using the usb cable not directly into the router.
I think overtime the usb connection point will become loose and will have difficulties connecting without holding it fame at position.
Im going to buy the sim one and will post the results here. Just give me time to order it.