I had looked at the wifi ranger, but the price is quite steep. You are paying for the simplification of wifi settings with their stuff. If you are comfortable configuring your home wifi router, you can consider getting a Unifi NanoRanger M2 + Ubiquiti airGateway-LR. That's a directional antenna, but those are typically the best for really pulling in a signal. There is a nice Youtube video to show you step by step how to configure it. I just bought a NanoStation M2 myself that I will wire up to a older home wifi router.

I also just got a Verizon Netgear Aircard 791L + Antenna to use as well. This device can provide a wifi hotspot, or can be a USB tether. I figure when I get to a campground, I will see which option works the best and pick that. If I ever find I need to have auto fall-over to another service, I will likely buy a wifi ranger router or something similar that will provide this service.