Well, the focus has some more aftermarket support than the contour even in audio, so it should bt two difficult to put together something nice.
Front Doors:
the Focus has prefabbed kick panels from Q-logic (I believe). They are somewhere around 100.00.
www.mmxpress.com has some crystal 3 way component sets that would work nicely in conjunction with the kicks (get the silk dome tweets not the titanium). They are 118.00.
Rear speakers: Crystal 5x7s. $69.00
HU: Like all cars, the HU is kind of a personal choice thing. The quality differences between the top brands are miniscule. I would probably lean towards the Nak CD45Z which you should be able to find for 300.00. Ad 20-30.00 for the adaptor plate to make it fit.
Another one to look at is the JVC SH99 (i think that is the model number). It has MP3 playback capabilities and a nice D/A converter.
Wiring: KnuKonceptz amp wiring kit. $? Guess 40.00...
Subs: Blueprint 1201 with Subzoneusa.com box number H-121. 130.00
Amps: 3 Planet Audio Tube amp from
www.groupbuycenter.com . 150.00 Each. 450.00
HU: 300.00
Doors: 200.00
Rear: 70.00
Wiring: 50.00
Sub: 80.00
Sub Box: 50.00
Amps: 450.00
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Total: 1200.00
You could save 150.00 by powering your rear speakers off of the HU.