Favorite phono stage in the $500-$800 range?

The Jolida JD9 mk ii is right in your price range. This is a tube-buffered phono stage with a great amount of configurability, with separate gain settings for LOMC, HOMC, and MM/MI. It also has a wide range of resistance settings for MC and capacitance settings for MM carts.

There are also some fairly inexpensive tweaks that are drop-in replacements--higher quality 12AX7/5751 tubes and better op-amps--that elevate the performance for low money and no soldering.

I used mine for 3-1/2 years and it's been really good. I only replaced it when I encountered a rare opportunity to get a MAGI Phonomena, which has been compared favorably to the Manley Steelhead.

The cartridge my have a loose connection or something, but otherwise, consider taking the money you were budgeting for a phono stage and use it to get a nice cartridge upgrade. There are lots of nice cartridges in the $500-800 range.