This is obviously a more difficult question to ask now, given 5th is on the way.
Essentials Dungeon Master Kit is way overpriced now, but the core rule books are still reasonably priced.
I don't care at all about premade campaigns or modules, I'd be making my own.
What player handbooks, rule books, dm guides, and monster books should I get for the most complete experience? (without having to pay over $150 for a complete set)