The kind I got were Derby Extra [1], and it looks like I was wrong about using up half of them over 3 years. I only used 1/4 (one-half of two packs), which comes to only a little over $1 per year.

They've been great for me, and have been the first and only brand of double-edged safety razor blades I've tried, so I have no point of comparison with other brands.

[1] - https://www.amazon.com/dp/B0032Q41LS