Hopefully you can just shop and get a better price.
I hope you have enough to just buy outright, unless you have Costco, and aren't that great at being a cutthroat negotiator: then use the Costco discount. Because you can use it on used cars but they have to be "Certified", which means they have an extended, in some cases 100k mile warranty.
BUT, if you've ever held your own and felt you got 'your' price in a back alley craft shop in Mexico...fight. Because you can sometimes beat the Costco price. It'll piss them off, but you could even do both: at the end suddenly remember "oh yeah I forgot: I need to talk to the Costco rep". That way you'll know you're getting the best deal, as they're legally obligated to show you the Costco price.
As far as loans go...I know it's anti-MMM but with the new car rebates and the 0% financing, a new car versus a car with 60k miles on it sometimes end up being $300 off. Which makes the new car a better deal, better warranty, better trade in value, etc. (Carfax judges cars on how many owners, etc.)
So...bring your calculator and don't just 'believe' anything you're told in a dealership: make 'em show you.
That said...if you're even halfway savvy you'd be better off not going through a dealer.
Good luck!