Where do you think the colonists got their guns from, and horses, and all their metal tools?

Sure, eventually they became self sustained, but at first a LOT had to come from Europe, and they needed to buy those things. The Natives would trade with them as well.

On Mars they won't have a lot of the resources the Americas had. They won't be able to even stay alive outside. They will need everything from earth at first. Then eventually they could maybe start their own economy.

But how? How much money will that cost? How much time? How many people do they need to really start making things worthwhile, or more sort of compound objects more affordable.

I mean you can buy a USB cable for very little money, but imagine if you had to make one USB cable from start to finish. From mining and refining the ore, to the complete product, all the factories etcetera.

That's expensive. It will be a long time before making a USB locally for the people living there will make sense, rather than paying the astronomical (literally) costs of transporting one from earth.

Eventually they could be self sustained. The difficulty, and what I might be able to see now, but with still many questions unanswered, is how it will get to that point.

How much money, with which industries, over what period of time? And what will life on Mars be like until then?