6.5in components for $400

The best answer to your question is your ears.

I can give you a few names, but thats what sounds good to me, the best way to purchase a set of components that you will be satisfied with is to go to your local shops, listen to what they have and compare

But to give you some insight, Nakamichi has a set for around 350-400, they are pretty crisp, MB Quart Reference series can be had for around the same I believe, alot of people like them, I find the highs are too bright for my liking, Morel's lower line are around 400, they sound good, Focal, polyglass are somewhere in that price range, while a favorite among alot of people, I have no personal experience with Focal, CDT has a few options to choose from within that range, though I have no experience with those either, I have heard alot of good things. Maybe someone else can add a few in for you, this is just what rings in my head right off.

But as I have said, don't buy a set of components from what someone is telling you, untill you have listened to them yourself, everyone has different tastes. Good Luck with your shopping, and hope I have helped.