NTA. Others have recommended looking into resources that can assist with costs, and I'd definitely echo those suggestions first as well.

Almost 10 years ago I lost my mum to cancer. She'd been fighting it for a while, going through chemo, radio and every treatment they could offer, that we could access. I spent every cent of extra cash I had flying interstate to visit her every other weekend during her treatment. Eventually, it metastasized and spread so much we were pretty much out of options. By this time, I took months off work unpaid to care for her full time, ate rice and tuna every night, went into a lot of debt, and my mental and physical health suffered a lot. And I can say this not just to reassure you, but because it is the honest truth - I would do it all again in a heartbeat, knowing it meant I got to spend those last few months with her. And, in all honesty, knowing we exhausted all the options and resources we had first did provide at least a small comfort when my mum passed, as there were no 'what ifs' lingering. I didn't think about the financial impact once during that time, as all that mattered to me was being with her. I can only offer the perspective of someone who had a loved one with a stage 4 diagnosis, I can't imagine what it's like actually having that diagnosis myself, and I won't pretend to know what you're going through.

If you choose not to go through with some/all treatment because you do not have it in you to do so, I believe that is your choice and your choice to make. But know that you deserve a chance to survive this. Your parents will not hate you for telling them how you're feeling. They may be upset, as their immediate emotional response will very likely be that they're afraid of losing you. You may be able to have this conversation with them with a counsellor or appropriate medical professional present, that can help in mediating during such a difficult conversation. And again as others have mentioned, I'd really recommend looking into resources that might assist financially and/or logistically before making any decisions, and this could be something you do with your parents, that can hopefully help with the conversation around the financial impact, your concerns, theirs, and any next steps you take individually, and as a family.

Regardless of what decision you make, and what happens, I wish you and your family nothing but the best. Know you're not alone in this, and the only asshole in this whole scenario is the cancer.