Newegg has Polk Audio PSW Series PSW10 Cherry 10-inch Powered Subwoofer: http://www.newegg.com/Product/Product.aspx?Item=N82E16882290035
for $89 using code: EMCKBJD66
Specs:
Type Subwoofer
Sold As Each
Driver Units 1 - 10" Diameter (25.40cm), Dynamic Balance Polymer Composite
cones
Power Rating Power Output: 50 watts Continuous Average Output
Dynamic Power Output: 100 watts
Frequency Response 35Hz - 200Hz
Connectors Inputs: Speaker level, line level
Outputs: Speaker level
Dimensions & Weight 14.38" x 14" x 16.13"
26.00 lbs.
