Judging by what your asking for, this is the cheapest one I found:
Profile HA1040 - 4-channel car amplifier
80 watts RMS x 4 - $119.99
http://www.crutchfield.com/S-DoJxw0CxUeq/cgi-bin/ProdView.asp?g=120&I=489HA1040
The Baja HA1040 4-channel amp delivers 80 watts RMS by four channels, or 225 watts RMS per channel when bridged to 2-channel operation plenty of juice for powering your system. The built-in variable high- and low-pass filters allow you to tailor the output for your system's particular requirements. You'll also find a selectable bass boost for the rear channels and treble boost for the front channels.
If willing to spend a little more, I suggest you go with this one:
JBL Grand Touring Series GTO75.4 II 4-channel car amplifier
104 watts RMS X 4 - $299.99
http://www.crutchfield.com/S-DoJxw0CxUeq/cgi-bin/ProdView.asp?g=120&I=109GTO754
A pretty cool feature is a see-through cover which if you want you could install internally-mounted neon tube for a cool backlighting effect. But anyway, the GTO75.4 II 4-channel amplifier incorporates an efficient power supply that delivers a big sound with low distortion. The variable frequency filters adjust the amp's output to best fit your system's specific needs, This amp has the controls conveniently mounted at the top which make it easier to set up and tweak it, while preamp outputs simplify adding another amp into your system. The preamp- and speaker-level inputs allow you to add this amp to almost any system, even a factory stereo.
Here are some of the details on it:
4-channel car amplifier.
104 watts RMS x 4 at 4 ohms (142 watts RMS x 4 at 2 ohms).
284 watts RMS x 2 in bridged mode (4-ohm stable in bridged mode)optional internal neon lighting (accommodates Street Glow AN9 tubes or equivalent, tubes not included).
variable high- and low-pass filters (32-320 Hz, 12 dB per octave).
bass boost (0-12 at 50 Hz).
MOSFET power supply.
preamp-level inputs and outputs.
speaker-level inputs.
CEA-2006 compliant.
fuse rating: 30A x 2.
Good Luck and I hope I helped.