I just went through the same process looking for a good home karaoke starter system that is not too expensive so below is my suggestion for $600 budget system:
$300 Player:
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Among the listed VocoPro players, I'd go with the VocoPro CDG-880 Pro ($300) as it is more versatile and comes with more features (DVD/DIVX/CD+G capable).
There may be better players out there in the same price range. Make sure to check/search on this forum for more recommendations from previous threads.
$300 Speakers:
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Option #1:
You can get away with a pair of Behringer Bi-Amp Powered Studio Monitor B2031A (not the new B3031A which may be subjected to quality issues) which has good reviews among the users. These speakers are small and portable yet can be loud to fill a small room easily.
Option #2:
However, I'd recommend to just get one regular PA speaker such as the Bi-amp Powered 250w Kempton GT12A for $300 shipped (via online quote request @ rmcaudio.com - ask Erik). This speaker is made by the acclaimed Italian FBT company - comes with 2 yr warranty.
Not only it is very portable, it has also plenty of power and reported to sound as good as the more expensive JBL EON series or Mackie SRM series from the vdrums forum users. Better yet, it comes with two channels inputs with independent EQ so you can plug your player/mixer directly to the speaker and that should work just fine for your simple setup. Besides, you can always add a second speaker down the road as needed and that would give you more flexibility in the future.
# Built-in amplifier: 200w+50w RMS class AB
# Frequency response: 50Hz - 20kHz @ -6dB
# 12" woofer, 2" coil, 1" driver, 1.4" coil
# Sensitivity: 97dB
# Max SPL: 121dB
# 38 lbs