I think you're missing that the feature we're talking about is specifically within the $5/month option, in much the same way that ProtonMail (the one I use), also hides their catch-all option behind a higher price-point.
I'm also fairly sure that they don't let you reply as the address the catch-all was placed on, which is an important feature.
If you know any that do, that'd be great.
True, I missed that "custom domain" isn't part of the lowest tier.
The point still stands though, if you have a mail provider that supports custom domains there usually isn't a limit on the catch all aliases you can add (or a very high one). In any case it's far from being "prohibitively" expensive.
> I'm also fairly sure that they don't let you reply as the address the catch-all was placed on
That is definitely possible with Fastmail as that's how I use it. In their case I believe that feature is called "Alias". If you reply to an email you just select with alias you want to reply from.
Almost every email host that supports custom domains supports receiving email with unlimited wild-cards. Is there something I'm missing?
Example: https://www.fastmail.com/pricing/ ($3/month)