About $3.50 each is a great deal and only $20.00 for the set. Check out the prices for a similar sized set here:
http://www.diamond-drill-bit-and-too...Drill/MAIN.htm
Try $291.00 !!!!
On the above posted link there is lots of useful information about using these diamond coated hole saws to cut glass aquariums as well as maintaining the bits and cutting other materials. This link should be a mandatory read for anyone cutting glass tanks.