I’m just going to speak as whole regarding all anime cels not just Pokémon.
Cel animation was used up until 2000-2001 so anything newer than that isn’t going to be done with hand pant and cels.
While most old school anime were 24fps that doesn’t mean it’s 24 cels per second. Even in the highest production quality you may get 6-12 cels per second. With main objects animated at 8 to 12 fps and background objects as low as 6 to 8 fps. Just go back and watch any old school stuff from before the year 2000. You’ll see that scenes are drawn out and that its maybe a still character(s) against a background that moves. It’s just smart animation to fill more time without having to draw so much.
Every Cel was hand drawn then hand traced and then hand painted. There’s no way they were putting out millions per Episode.
I’m regards to value there was a lot of cels produced so it would be common to think that they would be relatively cheap.
Value comes first from what is happening in the Cel, main character, cool, iconic scene etc. Next comes from wether it’s a Key Cel. These are typically the first and last cels in a particular cut of sequence. They are drawn by the head animators rather then just the fill in people. Look at the names of the head animators of some big franchises, they’re well know and famous so key cels can gain a bit of value.
Also having the original hand painted background adds tremendous value. A particular scene could have 100’s of cels against one background. A battle or fight scene is a great example of this. If you have a Cel from that great. But if you have the original background too well there’s only one so it steps up the value again.
The issue is that lots of the stuff just doesn’t survive. They are extremely fragile and degrade quickly. May companies reused the plastic sheets but simply cleaning off the old cell, on top of this a lot were just trashed. When your talking 10,000-100,000 sheets of paper paired with a hand painted Cel that’s a lot of storage and these weren’t worth anything just a few years after production.
Finally a lot of companies just don’t sell to the outside world. It’s the same reason why movies props and anything else used in production of media is scarce. The companies simply don’t let go of it.
A particular cels value is really based on a lot of variables and there is plenty of junk cels out there from unheard of shows for dirt cheap.
In my experience however even shows with a ton of stuff out there like Hunter X Hunter still have main character cels starting at $200 each.
For Pokémon I don’t see them often. They just rarely make it out of the companies. So they definitely have value.
Sorry for the long post, hope it helps let me know if you have any questions.