NASA has the concept of an earth-Mars shuttle system, which might consist of more than one shuttle vehicle continually going back and forth, as well as an earth-moon shuttle system. The idea of a transportation infrastructure would be intended for longterm discovery and development rather than a few one-off missions. That is, there would be regular transportation to and from the moon and Mars from now on. While it would cost something to set up, it should be cost-effective in the long run. Something similar would be done with respect to the Asteroid Belt by the private sector if asteroid mining is ever allowed.
Asteroid mining might be better done with NEOs, rather than all the way out to the asteroid belt.