Walter (the protagonist) didn’t start manufacturing drugs as the last resort to pay medical bills. From the get-go, Walter got offered a job by his former co-founder friend Elliott (who ended up turning their startup into a successful corp, while Walter ended up quitting and becoming a teacher), with the explicit mention of their health insurance being sufficient to cover any medical expenses Walter might incur.
That happened literally in the first few episodes of the show. Walter refuses because of his stupid pride. Later on in the show, Elliott and his wife straight up offer Walter to cover all medical costs (current and future ones), and he still refused. He had many many fantastic outs that didn’t require him to continue manufacturing drugs (or even starting to do so in the first place).
I am mostly upset about this inaccuracy, because it undercuts one of the most important aspects (if not *the* most important aspect) of the show. It is a story about a man who lived a life full of regrets, feels impotent, and found an excuse to do all the bad things that make him feel good, self-important, and inflate his ego to crazy highs, all without feeling any remorse whatsoever.