All CB radios operate at 4 watts of transmission power by the FCC. The thing that differentiates different models is the number of features. One thing to remember is that all CB Radios have the same transmission power whether it is a $60 model or a high end model at $300. A radio can be tuned to improve performance, but primarily have the same transmission out the box. Do the additional features warrant the extra money? That is for you to decide.
There is no difference when purchasing a CB Radio for base or vehicle use, the only thing to take into consideration when buying the CB unit, is the size and the antenna. There is a vast choice of both CB radios and antennas online but not all are good, so it is advisable to do some research before buying any. There are reviews websites, such as https://www.cdhpl.com/best-cb-antenna/, where you can compare different types of CB antennas from different manufacturers until you find the best one for your needs. Obviously a smaller CB Unit is going to mount easier in a vehicle. The most popular brands are Cobra CB Radio, Galaxy CB radio, Midland CB Radio.
One of the determining factors to decide is how the CB Radio Equipment is going to be used. Will you be using it from your home in a fixed position or do you need to be more mobile? These are a few things to sit down and decide before you go out and spend any money.