To get money, you can use the Vs. Seeker to rematch against trainers. Or you can sell items that you get from the Underground, though that probably takes longer and generates less XP.

You can often get the events via trade on pokewifi --- that's how I got the things there was no way I could get from a friend, like the regi trio. I'm pretty sure my copy are cloned, but I don't even care, because I was not willing to play a separate game for just three Pokemon.

You could get a Manaphy here still I think, although I don't know how much longer that will last.

The roaming legendaries are arguably worth burning master balls on. You can often get cloned master balls off of pokewifi too, or sometimes randomly off of GTS.