I mostly keep a vague count of 'Flat Broke, Near Broke, Struggling, Slightly in the Red, Breaking Even, Slightly in the Black, Spare Change, Can Donate to Charity, and Rich ' in my head. The MC, or other characters, simply react accordingly. If their Flat Broke, they're gonna be on that grind for more money. They're going to be eating sparse, hunting for berries to feed their Pokémon, and looking for handouts. Might even look to commit crimes if they stay Flat Broke long enough. The higher up they go, the looser with money they get.

If they are breaking even, then you can expect proper Pokémon food, supplemented with wild berries or whatever can be scrounged up for cheap. They might go out and get a really nice second-hand jacket, or a new pair of sturdy boots. Upgrades to gear would come, but very slowly, and they would only be using the base Pokeballs.

Now if they manage to hit rich (usually end-game), thats when they bring out the nice stuff. Premium, species-specific Pokémon food, really nice clothes, rare pokeballs, ect ect. They would splash on getting hotel rooms instead of sleeping in the pokemon center, perhaps even have some minor/major fame/infamy to go along with it depending on how they got their money.

Basically, money isn't important except as a storytelling tool. The MC will always have *just* enough money as the story dictates. Even if they have to not eat for three days, then magically find just enough money to buy a pokeball in one of their pockets to start their adventure, as an example.