Razors are practically, not quite, but practically caveman technology. I'd imagine that any products making it it to the modern market are roughly the same grade.
One thing I'm sure of: A good sign of a superior product is that it doesn't need monthly replacement.
This is untrue. First off, facial hair has different consistency (tougher, finer, curly, straight, etc.) and what may work for one person doesn't always work for someone else. Second, (as someone who has to shave every day) there's a vast and noticeable difference between safety cartridges; there are really bad ones out there.
Not even close, there is a huge difference between shaving with a $0.5 razor to a $4 one. I'm talking from experience. Apparently making good razors isn't as simple as it seems.
Not so. The technology invested in razors is significant, and their pricing has been studied to hell and back. Gillette is selling a very sophisticated product, and they test it thoroughly. It's a pretty fascinating business, actually. Despite the high prices of the top end blades, their price on a cost/shave basis is only slightly higher than cheaper blades - they last literally several times what the cheap ones do, and cut better the whole time.
One thing I'm sure of: A good sign of a superior product is that it doesn't need monthly replacement.