Looking for a cheap(below$150) off the shelf speaker that I can plug in directly to the PSR2000 for small room amplification. The on-board speaker is not enough power. Something I can buy at GC, Bestbuy or Circuit City or someplace like that. It does not have to be super high quality but decent enough to listen to and people can sing along with you. If I can get away with one (not a pair) would be great - needs to be lightweight. Will a monitor speaker work ? How about a small guitar amp ? Thanks.