That is a good question, so I went to staples, and found the cheapest of the cheapy disks they had (staples brand name, generic disks)
A pack of 10 disks is $4.28
http://www.staples.com/webapp/wcs/stores/servlet/StaplesProductDisplay?prodCatType=1&storeId=10001&catalogId=10051&langId=-1&productId=85880&cmArea=SEARCHA MUCH better deal is to buy their 100 disk pack (best deal they have, again using the generic Staples brand)
http://www.staples.com/webapp/wcs/stores/servlet/StaplesProductDisplay?prodCatType=1&storeId=10001&catalogId=10051&langId=-1&productId=14717&cmArea=SEARCHThe 100 generic disk pack is $25
So, using the 10 packs as an example you need to purchase 111 packs, which would cost a total of $475.50
Using the cheapest generic disks in 100 packs at $25 each, you would have to purchase 11 packs, and that would cost $277.75
And then of course you would have to do whatever it is that you do with adhesive tape to each and every disk to make them work. Oh yeah, and they don't come with games already on them.

I have to sell them as blanks for A) legal reasons and B) I don't want someone to purchase them, and be thrilled about 1,100 disks with games on them and then complain because 11 of the games don't work on his Amiga, for whatever reason.
The disks have all been stored nicely in a box in neat rows and when I turned on the Amiga and played a bunch of games with my kids, every one of them worked.
These aren't a bunch of junk disks. As far as I know they all work, but I think you guys are underestimating the huge number of disks here.
If I were to load one disk and test it out every 10 minutes nonstop it would take me 185 hours to test each and every disk (that's 11,100 minutes)... so if I were to do that for 6 hours a day (after work) it would take me 31 days to test each disk.
:-D So even for "blanks" the price is very good. :-D