The character and vehicle bonuses are all too easy if you know what you're doing. First off, you shouldn't have been spending money on buying any character in the store, since you unlock (for free) one character type (Imperial, Bounty Hunter, Midget Character) when you complete all the stories.

Secondly, you need to save up $900,000 and buy the Power Block Invulnerability. You can unlock that crucial block by locating it in Free Mode in Episode 4 Chapter 5. Once you leave the trash compactor, open the first "locked" door you find (it's a second trash compactor room). Investigate that room for your much needed cheat block.

Now you have the right tools (i.e., invulnerability), you can stick to using a bounty hunter and simply lob Thermal Detonators to blow up masses of enemies as well as the shiny metal objects that leave the $10,000 purple stud in the stages (for vehicle stages, some objects destroyed leave a purple stud). These objects (in character and vehicle stages) regenerate, so you basically "run a loop" blowing up the objects you destroyed and coming back to them later.

Lastly, if you have Jango Fett (PS2, Cube, and Xbox only) or bought Boba Fett, they are a good character to have on Episode 5's character bonus level, since they can simply jet pack over the gaps in Bespin. For the most part, you can jump (once) with any Blaster using character and shoot while moving to kill enemies and pick up studs. For $1 million, the blue studs don't count much (although grab them if they are in a pile), so go for the very rare purple studs extracted from destroyed objects.