Some automobiles can be towed four-down, some can't. Some can be towed with a dolly, come can't. There are various sites that will tell you about each car.
There are two types of tow bars: 1) mounts on the car. 2) mounts to the motorhome.
If you use a tow bar, you will also have to have a base plate which bolts to the frame of your car. Again, there are sites that tell you which one fits a particular car. Tow bars range from used at about $250 up to almost $1000. Base plates generally run around $250/$300. Installation can run up to hundreds of dollars.
Never used a tow dolly, so I have little information on them. However, prices vary from $500 to over $3000 according to Google.
I have a 16-foot flatbed trailer that I have used to haul vehicles over half the US, but never used it behind the motorhome. A flatbed ranges from about $600 up.
Then there are toy haulers. These are RVs that allow you to drive your vehicle inside them and haul them that way.
Hitch Trader is a good site for used items.
GM
My main problem with a tow dolly or a trailer would be finding a place to put them after setting up in an RV park.
