I disagree with many of the commenters regarding the concept of "Relative Wealth" not existing in the anime.
The show has directly implied Jame's family is exceptionally wealthy. We also have Giovanni, Steven & even Chairman Rose who have also been shown to be very wealthy through their attire, mannerism and general personality. The anime often takes the more traditional/Old money concept while displaying wealth; in other words, you don't see your T-shirt and Jeans Mark Zuckerberg type billionaire in the Pokemon Universe.
As for the case of Ash, in theory, yes you could argue he is currently in the perfect position to become very wealthy if he wants to. However, the wealth would more or less be generated through advertisements, partnerships, endorsement deals etc (Which all exist within the Pokemon Universe). However, Ash is unlikely to be someone who cares about any of this.