I'll give you my up-to-date recommendations first, and then some comments.
Der fliegende Holländer
Klemperer (EMI 1967) or Böhm (DG 1971).
Tannhäuser
Sinopoli (DGG 1988) or Gerdes (DGG 1969)
Lohengrin
Kempe (EMI 1963)
Tristan und Isolde
Kleiber (DGG 1982) or Furtwängler (EMI 1952)
Die Meistersinger von Nürnberg
Von Karajan (EMI 1970)
Der Ring des Nibelungen
Solti (Decca 1958-1965) or Keilberth (Testament 1955)
Parsifal
Knappertsbusch (Philips 1962) or Kubelík (DGG/Arts Archive 1980)
So, there are my current recommendations. However, Wagner's
oeuvre is so massive and so diverse that I'd caution against approaching it all at once. I'd recommend "best of" or "bleeding chunks" CDs at first. It's a good way to hear a good cross-section of Wagner or just the
Ring. Pick something like
Tristan or
Holländer, if you decide to jump in, work your way through the earlier stuff and
Meistersinger, then the
Ring and
Parsifal. It bears noting that there are a lot (no,
a lot) of Wagner interpretations on disc. Some are very faithful to Wagner's intentions, style, and music - read: conservative - and others have their own styles. You should sample and find the style you like the most. It helps getting grounded in the "classical" recordings, but you'll want more than that as time goes by. Wagner, too, wrote his "operas" as music-dramas, so you should get a good standalone libretto and familiarize yourself with the story and the action. Otherwise, you're missing half the fun.
Welcome to Wagner. There's no sense mourning your wallet now. It's too late.