What is a good turntable preamp under $500?

Yes, a Grado NM cartridge 

Pro-Ject Tube Box S2, add some good aftermarket 12AX7 tubes. 

Phono stages get dramatically better with cost. You will probably find a $500 Phono stage better. I have been unhappy with low cost phono stages.
 

You can get surprisingly good sound out of a few thousands of dollars of analog. I typically recommend the investment in the phonostage roughly equal the TT.  I had an old AR turntable which I was finally able to put in next to my contemporary TT (through a $17K Phonostage)… it sounded terrible. There has been huge improvements in TT over the last 30 or 40 years. 
 

For the last few years I have been playing the game of having analog and digital neck and neck. Digital was better until my most recent upgrade, where vinyl moved ahead a bit. Both are totally satisfying. You can see my system. 
 

Just some random thoughts. 

Darlington Labs MM-6 is all discrete and has zero negative feedback.

I would upgrade from a Pioneer receiver or save up for better speakers perhaps before spending money on a phono stage, but if that's where you want to put your money the Parks Puffin would be my recommendation at your stated budget.