To unlock bank 30 Jiggies at the bank, which are obtained by beating any challenge.
If you need help beating a challenge look at the leaderboards for that challenge. The top ten have replays of how they did it and sometimes you can download the blueprint of the vehicle they used.
You can also get jiggies by
- For every 4 T.T. Trophies
- Buy from Jolly Dodger
- Tampered Switches.