usually if your dealer offers financing you can get zero interest anytime of year, but if might cost you more.
When Watkins offers special financing deals if costs the dealers less than normal because they negotiate a better deal than the dealers can get on their own.
So to answer your question tell your dealer what you want in advance and have them work you out a price, just be patient, usually the same as cash will cost less than if you paid with a check
Everything beside cash/check, meaning credit card or financing costs the dealer and ultimately you more so just know that going in.