This is an achievement with a deceptively high ratio. It's actually fairly easy.
Early in the game - beyond the first tournament - you unlock Cash Tokens, which are yellow tokens with a nut pictured. When you combine two Cash Tokens, they become a x2 Token. Each power is 50 gold, so if the power is 5, then the total gold will be 500. If you combine this x2 with a third, it becomes a x4, which when activated (as long as its power is 5) will give the achievement.
How I unlocked it was I went back to the first tournament and fought one of the robots. These guys are very passive, so as long as you keep your defense at 10, they'll never attack. They will use damage tokens that chip away your health, so keep that in mind.
Then I stalled until I drew the three Cash Tokens I needed. It took about twenty turns of combining various tokens and essentially wasting them before I was able to draw the three I needed, but my opponent never attacked as I always had my defense stocked up.