The big delta-v is getting from an Earth launch pad to orbit. Everything after that is much cheaper. A fully fueled ship in Earth orbit can go to Mars, land, a

The big delta-v is getting from an Earth launch pad to orbit. Everything after that is much cheaper. A fully fueled ship in Earth orbit can go to Mars, land, and return. Same with most other round trips. Not to mention, fuel can be generated in the belt outside any noticeable gravity well.