Pleasure =/= self-benefit. Doing something because it brings you pleasure and doing something because it mathematically gives you more are different. When you perform an act of charity, it is because you value that act more than the selfish alternative. Read that again: YOU VALUE. You are acting out of a desire to fulfill your value. That is selfish.
It's worth saying that selfish, in this context, is not intended to be negative at all.
Helping those in need for personal benefit is entirely possible, thus your definition cannot be correct.
What do you mean by "truest self-interest?" It sounds to me like you are using it to mean "perfect world" or "ideal." Regardless, I say these men you speak of are self-interested. It is these men's desire to survive and earn the means to better their life that drives them to work, not society. Every act is affected by outside forces, of course, but in the end The values of society have little to do with a man's drive to survive or self-interest; they only help to create the environment that he has to work with in working towards this interest. In short: these men want money to fulfill their self-interest. Whether or not they have to work to achieve this is irrelevant.