Shop around, you can find some awesome deals these days.
Any of these amps would be a good value for higher end quality and solid performance:
AudioBahn Specials For a sub, I honestly believe you can find plenty of good sounding 12 inchers for under $150. I had one of the new HiFonics HZ series for a while, very solid sub and highly recommend it:
HiFonics HZ series subs But if you are looking to push some serious power to a single 12" sub, Orion HCCA or H2 and MA Audio XL or Hard Kore series top my list. I've currently got a single 10" XL with a HiFonics XI-Zues bridged mono to it and it's way more than my little Contour needs. Depends on what you are looking to spend, but I would shop for quality rather than a specific rating. Meaning you'll be much much happier in the long run with a lower rated higher end amp and sub vs. a cheaper amp with higher specs.