I’ll go from most expensive to free.
1. Satellite. You get a dish and it scan’s the sky for satellite internet, delivering it to you wherever you are. Even in the middle of nowhere. They have automatic roof-mount ones as well as big weildy pull them out and set them up ones. This is what I really want. If I had satellite and I could make a little money on the internet I’d almost never have to go to towns. But the set up costs are huge, you have to attend an inconvenient training, and I think the government might be able to tell where you are. Once your all set up ($2-4k) it’s only $80-100/month, and I’ve heard some people say as low as $50. This is a good article that discusses your options for equipment and service providers.
2. Cell phone card. This is what I did when I first lived in a bus. You’ll get high speed internet anytime you’re near a big city or on a major freeway in the lower 48. I had Verizon and it worked great for about $60/month. But if you’re near a big city or on a major freeway you can probably find wifi for free.
3. Free wifi. It’s everywhere, these days. Even in a town of 100 people I once drove around hitting refresh and eventually found wifi. You can get it free if you’re a customer at many coffee shops, fast food joints, even gyms. You can also park in close proximity to anyplace with wifi and hide out in the back of your van surfing on the downlow. Here’s a sampling of good places to find unsecured wifi: colleges, business parks, apartment buildings, hotels, neighborhoods where houses are close to the road, libraries, restaurants…. in short, just about anyplace people have computers.