I have a Wilson 3G amp with 13db antenna (about 30" long) that I used with a data card (direct connect) during the 2009-2012 period. It seemed as though my coverage was endless, except in NW OK with Verizon. I drove a big loop around Nebraska from York, to O'Neill, to Valentine, to North Platte in which we only lost coverage for a few minutes during that time.
I was able to get the amp for around $100 and the antenna for $40 if I remember right, but that was used 3G equipment. A good 4g setup, like what Gordon offers, is not going to be anywhere near that price point. If a great connection is that valuable to you, then I am sure it would be worth the money. Places like Kansas to SD, you will be hard pressed to find a place that amp and antenna can not get you coverage.