Ok. Since you asked. In car stereo, as with most everything else in life, you usually get what you pay for. There are exceptions, but that usually holds true. First off, I would suggest you find a reputable car stereo dealer in your area, because that is the way you're most likely to get good information as well as service and proper installations and all the other good things that specs and price tags don't take into account. You might not (probably won't) get the internet prices that you've found, but then in many cases there are a lot of good reasons to pay a little more for expert advice and service. Especially if you're inexperienced.
And please, please, PLEASE don't do the "I've-got-a-buddy-who-says-he-can-install-it" thing. Unless he really knows what he's doing, he can create a real mess. I've worked as a professional car installer for a high end stereo shop. I've seen a lot of disasters created by the "I've-got-a-buddy" thing. Some much worse than others, but I certainly wouldn't chance it. Especially if you're planning on getting a nice new car like, shall we say for instance, and RX-8?
Now for the opinions. Personally, not a big fan of Clarion amps. If you ignore the specs and just listen to the amps, they're really kinda wimpy. Also personally not a big fan of class D amps (or class T or H as some companies have taken to calling them) but I do see the value of them for sub amps. So for a sub amp, a class D amp can perform well enough. In the price range you're looking in, I'd suggest MTX or Crossfire. US Amps are also pretty good. All three of those, I'd consider amps that have a lot of power without being overpriced. Good values, how's that? I would definitely not go with a cheap crap amp brand, ie. Crunch, Boss, Jensen, Rockwood,... The list is pretty much never ending. If you do, then make sure you have a decent return policy. And don't say I didn't warn you. And for the love of all that's holy, do not get a Sony car amp. Especially if it's new, cause they're all junk now. They're actually worse than the crap brands. Sony makes some really good stuff... Car stereo amplifiers is NOT in that list. You've been fairly warned.
Ok. I'm done.