if my credit is 650 and i have a trade in worth 4,500 how much would i have to put down for the 2009 bmw x6

Depends on the lender. Get the price of the car you are looking for, get a pre approval from a bank and the difference is what you need as a down payment. keep in mind interest rates, a 650 score is not going to be the best of rates or the highest dollar value. i believe the x6 is about $45k or so right? so you may need up to $25k down total - from experience as a lender