Adam,
If you are planning on building your own cabinets, you might want to check out this site:
http://www.speakerbuilder.net
Unfortunately, there are no preassembled boxes available (yet), and I have not heard any of these designs, but I can attest to the quality and exceptional value of the Parts Express drivers used in many of the designs. I have used both the 5.25" Dayton drivers and the 6.5" in budget speaker projects a couple years ago (with Vifa D27 tweeters) and was amazed at how good they could sound! As all speakerbuilders know, exotic drivers are no guarantee of great sound, and with a clever crossover design (carefully tailored to the characteristics of the drivers) and a sturdy, non-resonant box, inexpensive components can yield phenomenal results.
The dayton tweeter seems to be getting some great feedback, and seems to be the equal of the Vifas I used at nearly half the price.
Three of the D3's up front and a pair of D2's in back, or 5 D3's should leave enough cash left over for one of the Titanic Subs from Parts Express.
If you have the ability to build some enclosures, I say go for it! There is nothing like listening to equipment you built yourself, and I doubt there are any commercial speakers for anywhere near this price that could compare in sound.
You simply can't find the quality of the Titanic subwoofer driver in a commercial product for under $800 (probably more) and the awful tweeters, cost compromised crossovers, and flimsy boxes found most budget commercial speakers are never going to be capable of the sound you can achieve from a good kit with a little (or lot) of hard work.
And I would also suggest looking for predesigned kit, as opposed to doing the Madisound LEAP-designed crossover thing. LEAP is an amazing tool, but computer simulation is only the first step in designing a great speaker system. Countless hours of listening, refining, remodeling, and more remodelling always follow-- Unless you have the test equipment and simulation software yourself, I'd opt for a kit where someone else has already put in all those hours.
Good luck with your project, and keep asking questions!

Mark