In my opinion, it is not worth paying somebody else to do. You will pay alot of money to do a very simple job.
I use my boat untill very late in the year, and start out very early, so my winterization consists of only changing my lower unit oil every year, and storing it with the motor in the down position. I also use fuel stabilizer year round.
The main thing is to change your lower unit oil, any moisture in there will freeze and crack the housing. Get the oil, the pump for the oil, and new gaskets for the plugs.
Fogging oil, easy to follow instructions. Keeps cylinders from getting any rust while sitting.
Store the motor in the fully down position. That will allow any water to drain out of the cooling system. I like to trim it fully up then fully down a couple of times just to make sure all of the water is drained.
Batteries. Topped off with water, and fully charged. I leave mine in the boat, with the charger running. It's best to unhook all wires for safety reasons while it is stored though. Never know when a switch will go bad, or a mouse will chew a wire.
Drain plug out to circulate some air through the bilge.
STABIL or SEAFOAM in the gas to keep it fresh.
I also re-pack my wheel bearings at this time. Having it sit over winter with moisture in the bearings will pit them up. Good time to do them to be safe.
Probably costs $20 in supplies, and you will have enough to do it for 3 years.
Steve