Which EDH staples are most worth the high price tag?

I've got about 50 dollars to spend on Magic, and I generally don't buy cards over 5 or so dollars but I'm looking to get some staples for my decks. I'd hope to get more than one card with my $50 probably.

A few that I am considering are Rhystic Study, Flare of Fortitude (not really a staple but is a nice cheap version of Teferi's Protection), some fetch lands, roaming throne, sylvan library, etc.

My decks:

Alela, Artful Provocateur

Ruhan of the Formori

Hazel of the Rootbloom

Ezuri, Claw of Progress