Speaker Replacement & Price: 1988 Volvo Station Wagon?

I have a 1988 240 Volvo Station Wagon and I wanted to get new speakers for it. I don’t want anything fancy or top of the line, just something that sounds better then the speakers that it came with. About how much would this cost.

from wal-mart you can pick up front and back speakers for about 100 dollars. not including installation, not sure about that.