Free: Contests & Raffles.
If those are the two you are choosing from I would go shoulder both and see which one fits you better. I would buy the gun that fits you the best with cost being secondary. If this is your first shotgun your hunting and shooting experience will be much better with a proper fitting and functioning shotgun.A couple of additional points, interchangeable choke tubes are your friend. Pick the right choke for intended quarry.You don't "need" a 3 1/2" gun. If you end up with one that is great but you can do very well without it.Good luck!
As others have said, a 3.5" shotgun is just for bragging. Most people who own them have never fired a 3.5" shell.