Man, is this a process I know well. I actually didn't give it as much thought as you are - it was more like my brain went "My kitty! Of course I'll do anything for my kitty!" And while if I had it to do over again, I'd probably make the same choice, it was really, excruciatingly hard. By the end, I couldn't go out of town, or even spend the night anywhere but my apartment, because she needed her meds and her sub-q fluids. The financial aspect, significant though it was, paled next to the physical and emotional cost. You're not just weighing her quality of life; you're also weighing your own.

You have given Boopsie a good life thus far. I think pretty much whatever you decide, you can do it guilt-free.

And one more thing - in my experience, hypertension and hyperthyroidism are actually pretty easy to control. Eliza got medication for her thyroid that came in flavored chews, and she loved them. They were like treats for her. And they worked really well, although it did take a little while to find a balance between controlling the thyroid and making her puke. She never lost her appetite, though. And the blood pressure meds, it depends on how easy the cat is to pill. If it takes half an hour of wrestling and cursing, that's a different story.

Good luck.