Might depend on your region, and whether or not the anime is currently licensed and in print. Stuff out of license is going to be all second-hand sellers, hoarders, and scalpers (at best) or straight-up bootleggers (at worst) which can cause asking prices to balloon.
Using your list, in the US:
Angel's Egg is out of print and may never have even had a US release, as far as I can tell. The ones being sold on Amazon appear to be second-hand resells of the original JP release.
Akira - $13.99 on Amazon / $26.24 on RightStuf and routinely goes on sale.
Ghost in the Shell - $13.99 on Amazon for 4k/BD/DVD / $17.99 on Rightstuff for BD/DVD "2.0" version that contains theatrical and a re-edited cut
Ninja Scroll is out of print. The original North American distributor left the market entirely, another company rescued it for a time, but the license expired.
The films still in print are totally normally priced. $15~25 for a film on BD is pretty ballpark for a major theatrical non-anime release. This holds up with newer releases, too, like Weathering With You introducing at something around $22 and being available now for about $15. It looks like classic Ghibli films (which used to be stupidly priced because Disney, but the license changed hands IIRC) can be snagged for around $15, too. At least that's the case with Princess Mononoke.
If you're outside the US, tracking down releases might be more difficult because I don't know if the markets there are as large, if there are publishers determined to keep older films in print. Even in the US it can be a bit spotty except for the biggest of titles (like Akira and GITS) which won't fall through the cracks.