That is the Catch-22
Unless you have some means of cracking food, water, energy and fuel from Mars, which, as they say in the engineering business, is a non-trivial problem, you have to have a steady supply train running from Earth like the Progress capsules to the Space Station. If you have transportation methods capable of bringing supplies from Earth and land them on Mars without breaking the bank, then you are also very close to having the transportation methods required to bring people home. Only the Mars-to-orbit link is missing.