Just to help with this conversation, "pikuach nefesh" translates to "saving a life". It is the concept in Judaism that saving (or preserving) a human life is more important than keeping a mitzvah. So for example if you are starving and you are offered non-kosher food, you eat the non-kosher food.
As much as I can think about mitzvot, strictly saying, it's almost impossible not being able to keep them because of the lack of the money - if you find yourself in that category at some point of your life, then you will be helped with tzedaka that was given by other congregants, or someone will help you to start working (a recent example from our community: a young man that was going to have his Beit Din and mikveh wasn't in the adequate financial situation and community payed him those fees in full).
Anyway, I think one should consult the rabbi on the specific problem one has in this case.
There should be someone to help within the community - at least it should function that way - we try to solve it that way in our community. We have a kosher kitchen and a solidly developed financial help system for the needy. I suppose that other communities solve it similarly, so no one would be brought to the point where he/she can't do mitzvot because of the poverty.