For another alternative - I recently picked up a Memorex Karaoke player at Wally World (don't tell anyone I went there - it was an emergency!) for $19.95 (US). AM/FM radio and tape player/recorder, about 2/3 the size of a soccer ball and about the same shape, and livid purple with silvery trim. Two mic plug input jacks.
Only problem is, you can't turn the amp on without turning on either the radio or the tape - but the tape deck doesn't really have to have a tape in it.
Sound is mediocre, but ok for boosting the mate's dulcimer. Works with a clipon tuner contact mic if you don't have anything else, although it's not very loud on that weak an input. I haven't tried it with a guitar or a real mic yet.
There are some pretty good sounding "real" karaoke boxes for a only little more - check out Radio Shack, maybe, or you might find one at a yard sale.