The monthly payment would depend on how much you put down/trade in. Thus $800/month is not really an exact figure you see!
The less mulla you borrow from a bank, the lower your payment. It also depends on the length of your finance.
There are plenty of websites that will give you a chance to calculate the monthly payment.
<a href="http://www.driverslane.com/calculators/calc.asp">Here's one example!</a>
Just put in the first 3 entries, roughly what you would think they would be for you, and the monthly payment will be automatically calculated. You have to make a guess in the finance rate. Don't be silly and put 3%, as no one will give you that. Go with 6-9%, and this depends on your credit history of course. Just to be more realistic.