Okay so the guides I've read so far aren't the most useful, here's the best way to get this achievement I've found.
- Step 1: Play through all 6 Episodes as normal, unlocking the campaign characters and achievements along the way.
- Step 2: Buy a Bounty Hunter Character, Droid Character, Empire Character and Ewok Character.
- Step 3: Hunt up the red bricks that provide the stud multipliers (x2, x4, x6, x8 and x10 all stack to make a x3850 multiplier)
- Step 4: Go to Episode 1 Chapter 4: "Mos Espa Pod Race"
- Step 5: Play through that mission multiple times, it's a 3 lap race and each time you play it you'll get 50,000 studs minimum without multipliers, with all multipliers you're looking at somewhere in the range of 192000000 - 192500000 each time you play it.
- Step 6: Buy all the characters
- Step 6.5: Don't forget to go to the Extras room and watch the Indiana Jones LEGO trailer so you can purchase him also. I believe he's 50,000 studs.
- Step 7: Enjoy you're 60G
You can also use Step 3 - 5 for the "Gopher" achievement.