Every goal he wanted (getting enough money to pay for college for his children, paying living expenses for a decade, etc) he met and still continued.
He even says so in the last episode, he did it because it made him feel alive.
The initial diagnosis is that it is terminal and without useful treatment options and his rationalization for cooking meth is to leave a nest egg. The high cost treatment comes up later and he immediately turns down an offer of no-strings payment in favor of cooking more meth to pay for it (Epsiodes 4-5).
The only medical service he pays for out of drug money before turning down the offer to pay for all treatment is the initial evaluation with the highly-rated oncologists that his wife schedules on her own without a clear plan of how they’ll pay for it from which the treatment plan originates.