Karaoke kits for less than $100 can be found at major department stores and usually include music discs and a mike. Here are some mail-order options:

KaraokeStar: Model RSQ CGK-70N was best overall at $269. It has plenty of controls to adjust music and vocals.
800-386-5743
www.karaokestar.com

Karaoke.com: Karaoke TV RX21 for $79 has good sound but the lyrics didn't change color dramatically on the screen.
800-USA-SONG
customerservice@karaoke.com, www.karaoke.com

Ace Karaoke: Model CAVS DVD-101G, for $269, had a DVD, CD and Mp3 player, but it isn't portable.
888-784-3384
info@acekaraoke.com, www.acekaraoke.com