What is a good turntable preamp under $500?

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. 

+1 for the Bellari VP130! Add a real Mullard or Telefunken 12AX7/ECC83 and you'll have a killer phonostage!

solid state:

darlington labs mm-6

ifi zen
newesst schiit mani-suppsedly it got better

solid state just over $500

audio by van alstine vision q phono

darlington labs MP-7

tube, including used:

pro-ject tube box s2,  under-$500 w/o/ tax, at least when i bought it, tho its prolly more now. goddam its real  good. 

heind ear 834p clone, $30o shipped w/o tubes
hagerman coronet 3
bottlehead moreplay