phono pre amp giant killer?

I'm in the market for a used phono pre amp. I'm considering the pro-ject tube box II and the clear audio nano (because of some positive reviews and the fact that I use a Clear audio Vertuoso Wood Cartridge). My question is how much do you need to spend on a used phono pre amp in order to get to the level of truly top flight performance? My budget was going to be 350 but that may change with this thread.

thanks
andy