Something I think people don't realize is why there's a runback. Primarily, it's there to teach you how to counter enemy attacks, especially common ones, and it helps you stockpile money so you don't need to farm for it. Usually, on the runback, there's enemies that drop rosaries. If you kill them every time, you'll get really good at fighting them and you'll get money each time, so the more you die to the boss, the more money you build up, which means when you do finally beat the boss, you'll have lots of money saved up, and can buy some stuff.

And don't feel bad if you are at 1 health and you have tons of money and you save scum and quit to go back to the bench and try again so you don't lose the money - it's okay, having to grind that money again is silly.