I love '80s music too! (which I guess is only natural since I'm on a '80s cartoons site- lol).
Amazon.com, Walmart.com, iTunes.com - those are probably some of the top sites I use for downloading music tracks- I'm not sure of the prices of all of them, but most MP3s are usually available for 99 cents each.
You also may want to check at Target- they have some great compilation CDs from various decades and styles- including the 1980s. I have gotten 3 different great collections of '80s music on CD there. 
Keep rocking the '80s music.
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