$250, new, with warranty
I run two of these, one to my 6 boat speakers, one to my Pro 485s. On my third summer with no issues.
They make funny little noises when the sound is turned all the way down, you can only hear it when it's quiet in the garage.
Cadence or Crossfire are also options but you don't get the efficiency benefits with class A/B amps.
I ran a HiFonics ZX6400 for the first few months I had my Pro-485s, it did a pretty good job. I had it mounted upside down, it shut down a few times from the heat so I replaced it with the Avionixx. The Avionixx seems to have a bit more power than the HiFonics, but not much.