Score modifiers are the best. Aim to get the red bricks that unlock each one, and also have all of the ones you've unlocked on at once. The purple stud which appears next to the shop normally gives you about 150,00 or so, so with modifiers:
2 x 15,000=30,000 2 x 4 x 15,000=120,000 2 x 4 x 6 x 15,000=720,000 2 x 4 x 6 x 8 x 15,000=5,760,000 2 x 4 x 6 x 8 x 10 x 15,000=57,600,000
Now that's a lot of studs! Unlocking all the characters/hints only costs around 4,000,000 total, so you're good to go.