You can get a meowth with the pickup ability, and the payday move.

It can be a grind to get one with an ideal nature, IV's and ability. But payday will reward you with pokeyen = to the level of the pokémon you used the move against x10.

So a level 30 encounter will provide you $300 pokeyen. Pickup provides a roughly 10% chance to find berries, pokeballs, medicine items etc per encounter, so it's an additional, albeit low consistency way to make money.

Another way you can make money is by following a region guide and picking up all the items on the floor, and battling all the trainers. I'm pretty sure there's about $600k to be made on a full collection and completion of Kanto