Bob -- If you're able to get a personal loan they usually come much cheaper than car finance deals, just compare the APR% before you decide.
Haggle the deal out before you tell them you're intending to pay by cash because they will not be earning any commission from arranging the finance, so get the lowest price possible for the car agreed beforehand, also get as much guarantee thrown in for free with the deal.
Don't let them pressure you into taking out their own extended warranty, if you require extended warranty it can be bought much cheaper from independent providers like Warranty direct.