Why are higher-ISO films often more expensive than slower films, and why does film cost more than photo paper?

Production volume. If you check closely, you'll see that low-ISO specialty films are also more expensive (sometimes considerably so) than the "default" 100- and 400-speed films. I used to shoot Tri-X and Technical Pan almost exclusively (in 35mm, medium format, 4x5 and 8x10) when shooting B&W, and Tech Pan (which had a continuous-tone sensitivity of between 16 and 25 ASA under most conditions) was nearly five times the cost (but oh, so worth it). These days the range of available films isn't nearly so broad, but it's pretty safe to say that shooting anything other than 100 or 400 is still fringe territory. That said, 3200-speed film is only a few percent higher in cost (here at least) than 100-speed, and only cents more than 50-speed per roll.

There's more to producing film than paper. Even minor deviations in dimension may mean that the film doesn't feed, won't be held securely or will not lat flat. Paper being out of dimension by a fraction of a millimetre means nothing. The sensitivity is completely different, both in terms of spectrum (panchromatic papers are expensive too) and actual sensitivity to light (you'd need kilowatts of light in your enlarger to get a 1/1000s exposure, and that would leave you precious little time for dodging/burning). Yes, there is less silver, but in real terms that's not a huge factor; it's the different compositions/structures of the silver compounds for increased spectral and absolute sensitivity that make the biggest difference. There is a much greater difference, really, between RC and fibre-based papers due to the cost of the materials involved. (It's hard to demonstrate the difference between graded and multigrade papers now because graded papers need to be bought in bulk packs and have become a specialty good; MG paper, which has two different emulsions, was traditionally more expensive than common grades, and it wasn't rare for Grade 0 and Grade 5 paper to be more expensive than, say, Grades 1,2 and 3.) There is no need for an anti-halation layer (the paper is opaque so out-of-focus rebound exposure is minimally destructive.). Nor are there spools, canisters or anything of that nature involved; usually just a box and (perhaps) a bag.

Those guidelines are for black and white, but colour is similar. Your film need to be much more precise than the paper (lot-to-lot variations in film are generally a lot less than lot-to-lot variations in paper).

Your hobby costs what it costs. If that upsets you, you can try making your own materials or try to find cheaper sources. If it's your business, pass the costs along. Or shoot digital—it's cheaper after a very short catch-up period (I'd average $4000/mo in film and processing costs in the '80s, which is only 20 bricks/200 rolls or about 100 finished 8x10 chromes) and it's mostly better as well.