If the walkie talkie is on the CB band, the only differences are range, built in antenna, and power source. CB's allow you to talk to most if not all of the truckers on the highway. A CB walkie talkie is about the same size as the first cell phones. You are looking at about $50 plus antenna for the type he's suggesting. IIRC normal effective range for these is 1/2-5 miles. FCC licensing is issued with the radio at manufacture.

The FRS radios are on an entirely different system. These are the ones that come two to a pack. These are generally smaller (about the size of a modern cell phone). The advertised range for these is 10+ miles. They work on two frequencies/power ratings. Licensing for the lower power channels is the same as the CB. You are supposed to send in a licensing form to the FCC if you will be using the longer ranged channels.

If you are talking car to car to coordinate stops, etc. I'd ask him why you want a built in model.

Unless you plan on trips like this on a regular basis, you might see if he has a spare or make him explain why a CB. FRS radios will be more useful around the neighborhood or amusement park due to their reduced size.