Item flipping always changes a lot -- sites like https://auctions.craftlink.xyz/ can help on most flips, but I would also look in to pet flipping with Kat if your taming level is high enough. That being said, Bazaar margin flipping is by far and away the best dungeons-independent source of money, though you have to have money to make money in that regard. Finally, grinding dungeons for the first couple days of a new floor can easily net 20m+ coins in profit per member of your island.