Unfortunately, I think you are underestimating what the converters will cost. Let's say it is really $30—which I doubt; we'll see come September because I am sure it will not be $30. You seem to be overestimating the ability of someone with a low income to buy a $30 converter.
It might not be a big deal for you or me, we won't go hungry that week. But there are many people without cable who have trouble just paying the rent. That is a fact. They struggle to make ends meet. Thirty dollars—and I am sure it will be double that—is an enormous amount of money for them. You cannot overestimate their ability to pay $30 for a converter.
You say people will go out and buy a converter, but how many people will need one? That is my question.