I suspect that much of the reason for the AF lens price difference boils down to this: Canon has always had autofocus motors in their EF-mount lenses, there never was an EF mount camera with a built-in focus motor. As such, they have a lot of really old AF lens models still in production, like the 50/1.8.

Nikon, on the other hand, has always had autofocus motors in their camera bodies. As such, their old lens designs, while as cheap as equivalent Canon ones, do not have built-in AF motors. (No need for one, they could just use the AF motor in the camera!) However, the consumer-level Nikon camera bodies made in recent years do not have built-in AF motors. And it was only when this happened that there was any reason for Nikon to start making lenses with AF motors (excepting some pro-level lenses that had built-in focus motors for added speed and low noise).

In other words, for a Nikon lens to have a built-in AF motor pretty much guarantees that the lens is a pretty recent one. A similar Canon lens can easily be a twenty year old design that is still in production. And new lenses are more expensive than old lenses, that is just how it is. If you compare the price on a recently designed Canon lens, like the 24/1.4L mk II, with the equivalent Nikon lens, the price is not all that different.

There is an upside to having a recently designed lens though: It is likely to behave somewhat better on a digital camera than an old one that was designed to be used with film. So you do get some benefits for the extra money.