There are three major choices:
1. Cellular data service, which you can get via a suitable phone acting as a modem (called tethering) or via a dedicated cellular modem, sometimes erroneously called an "air card".
2. Satellite based data service
3. Wifi at campgrounds, motels, restaurants, etc.
Cellular costs $50-$60 month depending on the method chosen and the carrier. If you choose the tethering method, it can be done on a day-by-day basis, while the dedicated modem method is on a monthly fee basis. Satellite is a bit more (I don't know the current figures) and wifi can be free or fee, depending on the location. Wifi is the least reliable method as afr as availability is concerned, but the price is right.
You will find numerous discussions about this if you search the forum messages for 'internet'. There are also articles in the Forum Library