Getting a minimum breeding population of 160 to Mars would require at least 70 million global hectares of resources (4.4 percent of world consumption, the average consumption of more than 290 million people, or 25 percent of what the U.S. uses). Even if we doubled this amount to help start a settlement, the investment would be a reasonable one, especially since it is likely to be spread out over at least ten years (resulting in an annual rate of less than one percent), and most of the resources would be used here.
Any settlement on Mars would need to quickly develop the means to locate and utilize the resources needed for its survival and growth, independent of Earth. Unlike our planet, Mars is totally devoid of biological infrastructure, so initially settlers would be restricted to technological processing of raw materials. In one or more centuries, using the methods of terraforming, settlers might enable plants, animals, and microbes to grow and provide basic food and atmospheric processing services.
If the population on Earth chose to continue growing in number, people here would ironically be working toward more, not less, technological processing of materials. While Mars became more alive, Earth would be going the other direction.