it’s expensive, you have to pay tolls, petrol, rent…will be taking a risk on the road, you will get lost on the road many times, so your travel will become longer and more expensive.
Your travel will become longer because of police or military, they like to stop private cars and if you are not colombian… they are curious to have a look to your bags.
Just use buses, they are cheap, safe, and comfortable. Enjoy Colombia, and it’s a nice country, just don’t make your trip complicated.