How much would i get?

I want to get a Ninja 250 but i had to repair my car (fine now) and dont have any money saved up for one. But i do have a 1998 Polaris Inday 500 sks. its and efi and we havent ridden it in 3 winters. It needs a new battery so i could do that and it would run fine since we had it running this past winter. How much do you think i would get from a dealer for a trade it and use it for a down payment. Or should i sell it privately and use that money for a down payment?