I think that the reason for the cheapness (relatively) of the 416 and 458 #1s is the market. A few people buy them because they think this is a DG rifle and it isn't. It is just a bad recoiling Big Bore. They try and sell them and the market determines the price based on level of interest, which is low.

As to how fast you can reload it, maybe twice to three times longer than a Bolt. That is if you don't drop the cartridge in your haste and are not wearing gloves that need to come off first.

You are right in commenting on the popularity of the single shot in the 1800's, before bolts rifles came on the scene, but they are all about nostalgia in the Big Bores now and are not a good choice for shooting things that bite and scratch in wet and or cold Alaska.