I honestly just cheat engine the money. And if I remember correctly... i didn't pay money for house in resort. it was something else.
I didn't and ended the game with like over a mil in the bank.
If you're trying to consume all the content added, you'll get it whether you like it or not. I basically had way more money than I had any use for.
Both DLC's also added a sort of arena/mass dueling mode. Each time you finish it you get a ton of money and those MAX status boosting items.
Completing both gets you 100's of thousands of money and EXP to level up your battlers.
To be fair though, the pokemon switcheroo arena mode took a crapton of time to finish though. You needed to get like 50 wins to finish.
I didn't need the money at that point at all, since I was already swimming in coin from finishing Main + DLC1. But I couldn't NOT finish it 100%, even though I'll admit it was somewhat frustratingly long.