NES

Get ROT. Seriously, once you have ROT the game is basically insta-win. You can the get the necessary gold fastest by repeatedly doing this process:

1. Save
2. Create ready made party
3. Move all gold to lead party member
4. Save
5. Create ready made party
6. Move all gold to lead party member
7. Save
8. Create ready made party
9. Move all gold to lead party member
10. Save
11. Create party with your main party's lead member, and the lead members of the above three parties
12. Move all gold to lead party member
13. Save
14. Delete the 12 characters created above
15. GOTO 1

Each pass nets 1200 gold, which would take a minimum of 12 chests to open normally, and probably closer to 20. Make sure to use the opening credits skip.

Also, get sands for your pirate battle before ROT.