I ran across this just the other day on Amazon -- 100 of my favorite blades for $8.24 with free shipping. Best price I've seen in a long time.
http://www.amazon.com/Derby-Extra-S...ef=sr_1_1?s=hpc&ie=UTF8&qid=1323445151&sr=1-1
http://www.amazon.com/Derby-Extra-S...ef=sr_1_1?s=hpc&ie=UTF8&qid=1323445151&sr=1-1