Joseph Keilberth's 1955 Bayreuth Ring, aka the real first stereo Ring, is on sale at the Berkshire Record Outlet for under $100.
This set boasts a terrific cast and remarkable sound. Astrid Varnay is Brünnhilde, Hans Hotter is Wotan, Ramon Vinay, Gre Brouwenstijn, Wolfgang Windgassen, Gustav Neidlinger, and others make it a vocal feast. That's about as good as it gets.
Click this link to see the first page of results at BRO. Right now, this set is at or near the top.