Start with your "in state" public colleges and universities. They are generally much less expensive for state residents than out of state schools and/or private schools -- and most of the state universities are of at least reasonable quality. Many (most) major state universities have online options now.
Going to a public out-of-state will probably increase the price tag.
Private schools are usually much more expensive -- and while some are of excellent quality, some private schools are run on a "for-profit" basis that focus more on taking your money than providing you with a high quality education.