Not sure you want to go to Bogota. If you have been there and know your way around, oh, yes, fun city, great places to go out and eat, cabbies are relatively chap, there are reasonable hotels, people can be friendly...
If you don't know your way, you might end up in the wrong spot and things can go south fast!
Try Cartagena (although expensive) or Santa Marta (much more affordable). For budget reasons I guess the flight into BAQ may be an alternative. Barranquilla is nice as well if you know where to go, again, but it puts it into 2 hour Bus distance from either of both other coastal cities.
Buses typically are good and cheap, as long as you stick to official bus lines (at the terminal de trasportes). They cover almost all the country and have become quite safe. Empresa Brasilia is the largest operator.