Mobile Radio Gear: (VHF/UHF only in this segment) Radios for Overlanding fall into two major categories. Handheld Transceivers (HTs) and Mobile Radios.
Handheld Transceivers are effectively "Walkie Talkies" and can run from as inexpensive as $35 per unit for a Baofeng UV-5R all the way up to several hundred dollars for a top of the line Yaesu/Icom/Kenwood digital HT, like this Yaesu FT2DR. HTs typically offer several power settings, with Low being ~ 0.5W, medium being 1-2W, and high being 5W. At 5W the radios tend to get hot while transmitting a lot, and the batteries don't last long. (It's worth noting a CB maxes out at 4W in the United States...)
Mobile Radios come in three major varieties, and then have a host of options. The three major types of mobile VHF/UHF rig are:
Single Band (usually 2M)
Dual Band (usually 2M/70CM)
Dual Band CrossBand Repeater (usually 2M/70CM)
The single band radios are exactly what they sound like. These radios operate within a single band, which usually means 2M, although they don't have to. These usually, but not always, output between 5w on Low Power and upwards of 75W on High.
A dual band radio is virtually identical to the single band radio, except you can select between two bands. This means if you're in a small group, and if everyone has dual band, you can select which band you want to use. The 2M band is the most popular band in the world. If you're looking for a quiet place to talk within your caravan, you might choose as a group to move to 70CM for instance.
Finally we have CrossBand Repeaters. These are also dual band radios, but they have two receivers in them, rather than one. This means they act in many ways as if you have TWO radios at the same time in your vehicle. These include a special mode of operation though, that allow you to "connect" the 2M radio to the 70CM radio. Thus, anything received on the 70CM side will be instantly re-transmitted on the 2M side. And anything received on the 2M side, will be re-transmitted on the 70CM side. When coupled with an HT, this can allow you to use the HT on 0.5W on 70cm, but communicate with a remote station using the 50-75W 2M transmitter in your vehicle. (Ask me about "Red River Gorge" in Kentucky sometime.)
Digital Mobile Radios Another newer entry into the Mobile, and HT ham radio market is Digital radios. These all operate normal FM like the others listed, however they include some form of digital encoding. Right now there are no "standards" so each vendor has their own competing protocols. Yaesu appears to have the most widely adopted system with C4FM FDMA and their Fusion Repeaters. This is a fairly in depth discussion on its own, and I'd be happy to field questions to the best of my ability but won't muddy the waters here.
Like everything else in life, in many ways you do get what you pay for. I personally intend to pick up a few (5?) UV-5R radios to keep in a Pelican case in the truck for dire emergencies but wouldn't personally trust them as a primary radio. Ham radio is like a lot of hobbies. There are many different ways to participate and enjoy the hobby. I've hardly scratched the surface here. I, and I suspect the rest of the Hams on Overland Bound, would be happy to field any discussion on the hobby you might have.
Single Band 2M Radio
Dual Band 2M/70CM Radio
Cross Band Repeater
Yaesu Digital Cross Band Repeater