I have never believed that the Harbor Freight blades are as good as those made specifically for quilters. Some quilters like them, but others have complained about them being relatively dull and/or inconsistent in quality. For someone with poor vision, I'm not sure they are a good option because you may have to press harder to cut.
What I have done in the past is bought in bulk from eBay. There are some "generic" blades there that are very inexpensive, but the ones I have opted for are the name-brand Olfa blades.
Here is an example of the "generic" blades on eBay (10 blades for $8.45, free shipping):
http://www.ebay.com/itm/10-45MM-ROTA...item1c3ce898d0
Here is an example of the "lot" size I usually buy on eBay (15 blades for $30, free shipping):
http://www.ebay.com/itm/Lot-3-15-OLF...item51c3cbffc1
Edit: I just realized that at least the second example above is still in the bidding process. What I usually do is click on "buy it now" to compare prices. I used to be able to get large lots of Olfa brand blades for about $1.50 each, but now they are running about $3 each.