If you get a portable satellite radio, you can move it from vehicle to vehicle and even put it in a portable boombox radio. It will be just one monthly subscription fee, but there are two drawbacks. First, the audio quality isn't as good as a dedicated digital radio because the portable units plug into existing radios in analog mode only. Secondly, if you move from vehicle to vehicle often, moving the satellite radio would be a real pain.
We have 3 subscriptions. One for my truck, one for my wife's car and a third for our home stereo & boombox. The additional subscriptions are less than full price, but still costly. But we enjoy our music and in Montana, there are not as many terrestrial stations and lots of places where there are no radio stations available unless you have satellite radio.