Probably not for less than you could buy one!, the mixer part is simple enough (opamps etc.), but the power amp uses expensive devices, heatsinks are expensive, transformers are expensive, large electrolytics are expensive!.
I've just ordered a Behringer mixer amp, 10 input channels, 2x400W, either stereo or mono + monitor, with two digital effect channels - it's £209 plus postage, I've seen it advertised for $349 in the USA.
What are you actually wanting to do with the amp?.