Yamaha PB1 used in nice shape , $300
Demeter HBP-1 used in nice shape, $550
Pearce BC1 used in nice shape, $ 425
A new Tech 21 RBI OR RPM about $400 with taxes .
Me, I like to add subtle to medium tube overdrive to my tone. For that I highly recommend either the RBI or RPM. The RPM has less tonal coloration than the RBI, and can produce more distortion on the far end of the dial. Still, I give the nod to the RBI. To me, the presence control is magic: it adds aggressive zingy grit on the top end, especially valuable with my tweeterless Bergantino NV610 cab.
I owned the Yamaha for awhile. It has great features, but is too polite for my taste. Good choice if you want clean and flat.
I haven't tried the Pearce and have too little experience with the Demeter to comment, but both are well regarded.
In short, they're all nice pieces of gear. The question is, which will work better for you? You're already figuring that out!