Turbo Mike:
Check the trendy cities in your area. In other words where GEEKs hang out.
Down in Mass they have a bunch of these shops in Boston & Cambridge mass near HARVARD EDU.
Shops like this amaze me to see they still keep rolling selling records. However they won't pay you retail because they need to re-sell.
Ebay would be a hassle selling 1 by1
I would group 10 at a time
or make a LOT for the same band.
Toss the cassettes or sell them in 1 big bunch on ebay $5 for 100 cassettes. You will come out with $$ for a 6-pack this way.