Base amps are going to cost ya a little bit more since they have their own power supply...Not many guys building base boxs, I think BBi is, and Davemade Mobi has some Davemade Base Amps listed, but your going to pay out the wa-zoo for one... XForce use to build decent base amps, but they are gone...

For the base, I run old tubes amps I found on ebay like the Palomar 300A and a R.F. Linear "Kicker 500", things are 30-40 years old and still kicking! Tubes have got a little pricey now, but they last forever it seems like.