The best way to make money is to go to a place where strong pokes appear and start to train there. They usually drop more poke$ than others. You can also try to catch a rare 1 to sell it (if it has good stats) or use covet on pokes that may have items, so you can sell them
Other tip to catch pokes use a watchog, with superfang and Hypnosis. It will be much easier, i catch every poke from 1 pokeball. (star piece = 9k) (don't know where to sell them on johto, on kanto is next to bill's house) Hope I helpped you with somthing! :Grin: