Cheat engine. Make your money infinite, buy all the coins you want, and buy Trapinch.
But of course, if you want to go the harder route, you could grind those voltorbs.
You could also try pressing C all over the place and pick up some coins.
Though Flygon isn't really worth it later on. I mean, the whole being dragon/earth with levitate is pretty nifty. But you'll start running into ice pokemon and a few dragons that can trample on Flygon. The process that it took to level Trapinch into Flygon without cheating was just boring, since Trapinch doesn't learn many strong attacks (maybe Bulldoze, but it was mediocre. ) The secondary evolution isn't all that great either.