Easily done with 3 AI players. Just play through the Hobbes Caves level in Dark Albion, on normal difficulty. Make sure you have the most gold at the end of the level, and you will unlock the achievement.
Tips: If you are struggling, try smashing extra crates, as well as fences for extra gold. Try to pick up any coins you can, as the AI doesn't use them as a priority. You can also buy abilities through the abilities board for your character, that will increase the amount of gold you attain, as well as your multiplier.