There are also inexpensive speaker setups to hook up to a TV, computer, or CD player that sound good - easy to identify if you just use the wealth of information out there to figure out what the marketing crap is and what actually sounds good.
If you have the time, would you list some?
I've got a spare parts stereo that works really well. At some point, it may need to be upgraded to something with fewer features and more raw power, which would then be connected to four studio monitors in a large room.
That, I've found, produces the best sound. Bass-box optional, if you need the extra blast it's great.
I like the little satellite speakers for the high end wheedly-wheedly sounds but studio monitors do OK on those too.
Sure, just keep in mind that they won't match up to buying old/used stereo equipment. This is mostly for desktop/office/bedroom use without a subwoofer, I've never bothered with a separate subwoofer as I've had two big Pioneer speaker cabinets and a proper stereo for the cave for over a decade.
Harmon Kardon made some speakers that came with Dell computers which you can get for around $20-30, they're small but have a pretty good range and sound. These are good if you don't want any boom from the bass that can be heard in other rooms. I don't think these were sold in retail and I'm not sure the original price from Dell, but there are plenty of them around. I have used these more often than not for smaller speakers for many years. http://www.pcplan-it.com/harmon_blk_speakers.jpg
Logitech has decent, cheap speakers but they tend to rely on subwoofers for bass so they're a bit lacking for most death metal. Altec Lansing has been similar for their retail line. I wouldn't touch anything from CA (cyber acoustics) or Bose.
As far as any speakers that require an amp, thrift stores are the best way to go to get good speakers cheap, though I've heard good things about the Micca MB42 and Monoprice's speakers. Haven't heard them myself that I recall, or haven't paid much attention if I have.