A lot of dealerships will give you a hella hard time paying in cash. They get a lot more incentives to have it financed with a lender. Therefore they pass some of those incentives onto you in the form of a rebate. For example, you can buy a 30k car in cash and pay 30k or you can finance 30k over 3 years and get a 2.5k rebate if you stay in the loan for 3 months. Then pay it off only accruing maybe 100 in interest and you essentially have a free $2400 discount.
Just don't be stupid and get an extended warranty.
ok so in that case i'd just do that and pay it off after 3 months...either way doesnt really matter for these calculations ---