College admissions are competitive. They choose candidates that they believe have the highest likelihood of success (namely graduation). Finishing and excelling in high school is considered one of the best predictors of collegiate success. If you have an astronomically high ACT or SAT score this would help. If you have a life story that shows that you have triumphed over adversity this too could help you get into a good college.
Most community colleges have open admission. Successfully completing a year or two of community college demonstrates commitment which can work in your favor. A lot of people who are F ups in high school buckle down when they grow up but it is an uphill battle to convince people of it.
Financial Aid and scholarships and a job. Save up your money and apply for every scholarship out there. Talk to a college counselor too.
You could always start out at a community college and finish your general requirements for much cheaper and then transfer to a better college after that.
if your good at what your persueing and i mean great at it often times businesses will send you to college in return for you working for them.