Get something with a headphone output so that you practice late at night or without disturbing others.
The best use of money somewhat depends on what you have available in terms of headphones and computer/stereo setup, too. For example, I have a small practice amp which I bought for very cheap (old Roland 30W amp from the 80s, $30 off craigslist) which sounds pretty decent, but I play through the computer almost 90% of the time while practicing because I already owned a nice set of monitors+subwoofer for the computer and a USB interface for a regular guitar. My nice headphones or computer speakers are much better than any amp in a low price range. I can also play along with a song using the parametric EQ function in iTunes to kill the bass output of anything in a playlist, which means I stay engaged and playing for longer.
Anyhow, I'd look for something used unless you already have a good stereo/PC interface where you're going to be doing your practicing, and then I'd strongly recommend buying a USB audio interface instead of a "throwaway" amp that you'll later ditch.