Cassette players are becoming more difficult to obtain as the medium progresses to becoming a relic. However, they can still serve their purposes, so if you're in the market for one, the best place to start looking for one is garage sales. Many people do not throw out/recycle their electronics in a timely manner, and certainly will appear in a garage sale even today. With minimal effort you should likely come across a cassette player for next to nothing. Otherwise, online used merchandise websites like Craigslist is another option for finding one.