I bought a hole saw on eBay for about $10 delivered, but it hasn't arrived from Hong Kong (seriously) yet. The seller's ID is "lau***" and he also has an eBay store, "THK Diamond Tools" (I have no affiliation with either). I don't have the nerve to drill my display tank, it is for sump and refugium work. From what I've been told these cheap saws are only good for a few holes, but $10 for three or four holes is better than $20 a hole.