Amazon has the 4-Pack Avery Marks-A-Lot Permanent Markers (2 Black / 1 Red / 1 Blue, 07905) on sale for $4.03 with free shipping on $25+ or with Prime (extra 5% off for 5+ S&S orders). 

Need a bunch? Amazon also has the 24-pack (20 black, 4 red) on sale for $13.59. (Roughly 57 cents each)