For just playing along with music (not mixing/recording music), you can find a pair of powered speakers for under $100 - there are many choices by Mackie, Alesis, setc:
https://www.sweetwater.com/c405--Act...itors/low2high
You can probably find a used set somewhere for half the money. Your computer should have an external 1/8" stereo jack, the speakers will come with a cable to plug into the computer, then another one that runs from one speaker to the other (powered speakers in this price range tend to have an amp in one speaker, and the other one is passive).