John,

The cheapest full range powered speakers for performance - which is what you want if I understand correctly - are keyboard amplifier packages.

zzounds selection: http://www.zzounds.com/prodsearch?q=keyboard+amp&form=search

Sweetwater selection: http://www.sweetwater.com/c525--Keyboard_Amplifiers/pn1

Another option are powered mains that can be used as well, but they don't have the controls that keyboard amps provide:

http://www.sweetwater.com/c134--Active_Powered_PA_Speakers

The exception is that Behringer with the 3 channel mixer built in - that's actually a cool product - I would call it a keyboard amp!

-Scott