Ever wondered why certain metals are expensive? It is all due to scarcity. However, many of these metals are in absolute abundance in the Asteroid Belt. Asteroid mining, will be a complicated feat. If all odds are beaten, once a company successfully, brings back tons of platinum and possibly gold then I guarantee that our species will enter a new economical and space-faring era.
Fuel is not an issue, water can be found on many comets and asteroids in the solar system and well as Helium-3. Using complex chemistry, the water can used drinking water, air and fuel. Helium-3, a potent radioactive substance found on the surfaces of the Moon , Mars , comets and asteroids can also be a fuel source . If you use probes instead of astronauts, you will save on costs as well.
The amount of Platinum in the asteroid belt is estimated to be about one billion Dollars for every person on the planet. However, all asteroids are created differently. There are C, S and M types of asteroids, all of which are classified by composition of certain elements like carbon and precious metals.
Below are some links to more information on the subject.
https://www.space.com/15405-asteroid-mining-feasibility-study.html