Being as this has used the Marvel Cinematic Universe tag as one of the tags, I will answer with a Marvel Cinematic Universe answer.
We haven't seen that many superheroes in the Marvel Cinematic Universe so far. Including the films and TV shows, as of March 2015 it would seem that the most financially insecure hero would be Dr Bruce Banner, who has no home that we know of, has been on the run from various agencies for a number of years (and as such has few possessions) and has no stable financial income.
The last time we saw him was in the post-credits scene of Iron Man 3, which gave us little to no information on his current situation - before that it was in The Avengers/Avengers Assemble which showed us a man living in hiding in an out of the way area of the world. In comparison to his team mates (a billionaire, a prince and three SHIELD employees), it would appear that he is the worst off, at least from a financial perspective.
Another potential candidate from the Marvel Cinematic Universe is Dethlok, but being as his history and current situation are a lot more uncertain, it would be hard to say for sure.