I get changing a rule or two here or there, but the books are expensive. If you're going to ignore 70% of the core rules, ignore 70% of a less expensive game instead.
There's all sorts of ways to gain access to the full 5e and 5.5e ruleset for free on the internet. Spending money is only required if (a) you like possessing the physical books, (b) you and your friends play in person and find sharing the book at the table more comfortable than consulting a website/PDF, or (c) you are a lazy fuck who really can't bother with writing their own character sheet and need DnDBeyond to do it for you.
I played 5e for half a dozen years before quitting (because of how disappointed I was with the OGL debacle and the 5.5 update), and I never gave them a cent. Since we played a heavily customized campaign with homebrew ruleset, classes and subclasses, I never felt like they deserved my money.