The internet will always be the cheapest place to buy an item that needs no support and no returns and can wait 2 days to get. I don't for a second think that most things aren't bought online. I price my store to be competitive with online prices as a convenience for them. If I had the option, I would be live goods only.
I know myself I have paid more for an item on amazon than grabbing it at say best buy or staples, because I forget to pick something up and if I order it right at 2am in the morning, it'll be here in 2 days no matter what, so convenience is where my life has taken me.
When it comes to the price of the diamond hole saws. I've bought them as cheap as $4 before. I paid $6 each for a faster delivery, and the ones that are coming from china were $5 each. On Sunday I would have walked into any store that had what I needed and paid $10-$12 each. However I won't pay 10x the price because it's in stock, knowing that I need multiple of the item.
I view all retail stores as a gas station convenience store now. No one stops at a Arco gas station to get the cheapest 20oz soda, they buy it because it's close and it's cold, and it's quick. Otherwise they'd go to a real grocery store and buy 1 for cheaper, or a pack of them for even cheaper.
A fish store is no different. Dry goods are there for convenience. I expect every customer to buy based on convenience.
For me, it is more convenient to wait 2 more days and save $68 dollars, than it is to get those tanks drilled that day. However if my battery goes dead on my car. I'm paying whatever price the store asks so I can get to work as waiting for one in the mail is not as convenient for me.