I just ordered a bunch of Schick twin injector blades from an eBay seller, but I misread the ad. I thought I was buying 32 blades (4 packs of eight) for under $30, but it turned out to be four packs with two blades each. I checked other completed sales, and found that the price per blade was all over the place, ranging from roughly $1 a blade to $20 for a pack of four blades.
To me, the standard for comparison should be the current Japanese Schick twin blades, which are are about $1.50 per blade. But there seems to be a lot more randomness than there seems to be for, say, Personna 74 blades.