Cheddar is slang for Cheese, which was already slang for money. I think Jay-Z is the one who first one to extend the slang "cheese" and make it the slang "cheddar," but I can't say for certain 'cuz I'm pretty uber-white.
from Jay-Z "Ain't No Love (Heart of the City)":
Whassup y'all niggaz fed up cause I got a little cheddar
and my records movin' out the sto'?