Well, first of all, there's the question of what you're using it for; second, there's the question of what you consider 'good'; and third, because the first two vary so much, the 'bang for the buck' is all but imposssible to assign. For me, the C-Sonnar is the easy winner, because it's the only 50 I like using. Others hate 'em. And personal stories of price are of limited value: I've been given a 50/1.4 Super-Takumar on a Pentax SV (a better lens than the 50/1.8, in my experience) and a 50/2.8 Tessar on a Contaflex BC Super.
As for Breathstealer's challenge, 2,9/50 Meritar and 1,9/58 Meyer Primoplan, unless you like 50-58mm portrait lenses.
Finally, there's sample variation, which is unlikely to have decreased in however many decades an old lens has been available.
Cheers,
R.