I've been looking into some different options for components and speakers for cars and ran into this forum.
http://www.diymobileaudio.com/forum/index.php Pretty cool stuff there. You can build a component speaker set from home audio and highend companies like Seas, Scan Speak, Morel, Vifa, etc... for less than most decent car component set's, and have MUCH better sound for alot less money.
This thread right
HERE explains the benefit of using 8 ohm drivers.
For an example of a lowpriced DIY components you can use an LPG 25nfa, with a Seas L18RNX/P Mid. It would end up costing ~190 plus shipping.
http://www.diymobileaudio.com/store/store.html LPG-25 each.
http://www.madisound.com/cgi-bin/ind....8109&pid=1037
Now keep in mind you need to use an active crossover, from either the headunit if it's adequate or from the amplifier, or from an electronic active crossover. And typically a 4 channel amp for the component set(one channel to each speaker), or a seperate tweeter amp and a seperate Midbass amp.
A couple of different headunit's that are capable of handling these crossovers are the Pioneer Premier DEH-P860MP, DEX-P9/DEQ-P9, higher end Alpine headunits, cda-9853,9855 is a good choice, Eclipse 8 series headunit's with promode. Clarion's DXZ955MC,DRZ9255,
I like the Pioneer for the price out of those, but an Eclipse or Clarion, is nice if you have the money.