Imagine the wealth a company could amass if it succeeded in terraforming mars. Rare metals, sale of land etc. This is one of those markets where you have rather high barriers to entry.
Metals: choose an elemental metal you think is rare. Look up it's Wikipedia entry, and look at its availability. It will be expressed in terms of a percentage of the earth's crust, something like 0.01%. Multiply that by 2.6*10^22 kg and realize that we're not going to run out of it any time soon, nor is it rare. It may be expensive to mine, but compared to the cost of transporting on rockets? Cheap.
Land: you can buy prime farmland in Saskatchewan, Canada for USD500 per acre.