Older 50s were a fabulous collection of very different lenses with very different drawing styles, uses and characteristics. I often wish many 20-30 something photographers could jump in the wayback machine to experience them firsthand.
All those mentioned thus far are excellent in their own ways - lens aficionados are going crazy with the a7/a7r series as they now have a great digital platform to assess and enjoy these lenses all over again.
Rather than identifying individual lenses - because many makers made not one but 3, 4 or 5 50mm lenses (fast, moderate, and budget, plus macro) - look into Canon FD, Pentax SMC, Minolta, Contax Yashica, then - as you have not said what you are actually looking for - consider the macro lenses, Nikon's 55mm, if you can stretch a little, Leica's 60mm f2.8 will walk away from almost all modern 50s for flatness of field, distant detail and colour.
For those familiar with MTF data charts, see here for the amazing flat lines at middle apertures, no distortion...it would be the envy of many makers today:
And many older manual midzooms are better at 50mm than many 50 primes at the expense of lens speed, but the good ones are more about $500-600.
It's always a good idea to know what lies ahead when money is less tight so it was good to read Gary H's thoughts. Dreams are important. good luck.