As far as where to buy cassettes, you can't do better than a thrift store. Not every thrift store stocks them, but if they do they will be cheap. Also, many used record stores stock them, but you'll pay more on average. I also find cassettes to have a very fatigue-free sound! I recommend only the commercially recorded tapes that you used to buy at a record store. The quality of homemade tapes is simply too unpredictable.
