Before spending too many studs, save your cash and purchase the x2 Studs cheat, then the x4 Studs cheat, and so on. Activating the x8 Multiplier and the x10 Multiplier will earn you a x80 Multiplier in-game.
All of your unlocked Red Brick cheats can be purchased here.
How to Get Infinite Studs With Multiplier Cheats