...impossibru?
Okay, whatever. I'll say my solution because it may not be possible after all.
You have only $5 to spend with one buy, and you have to go ahead and buy a Province, right?
Here's what you have in hand: Silver, Silver, Quarry, Watchtower.
Play treasures, buy Traveling Fair, $3 left to spend. Quarry cheapens action cards, buy Cultist, trash with Watch tower, draw 3 Platinums, buy Province.
It's probably not possible because I don't know if you can play treasures once you actually buy something. I don't think I even need a Donald conformation, it doesn't work in MF or Goko now that I think about it. So yeah, not a real solution.
I'm not good at this puzzle thing at all.