You can get this at the end of the first real level when you have collected all the little glittering orbs in the level (some kind of dockyard?). The level will end with a fight with your dragon. Before this you can select the dragon (you'll only have one). Some cards and when you proceed you will come to the menu where you can buy upgrades. The cheapest one costs 3.000. I had exactly 3.000.
You will need to buy all upgrades for all bakugans anyway for this achievement:
So just go ahead and spend the money. If you don't have 3.000 simply play the next level (takes less than 5 min). And buy the uprade then.