In 2013, bought a trailer sailer built in 1976. So far, the maintenance costs have been about $25 to replace a tired tire on the trailer, $15 to replace fraying main halyard (I left the metal wire portion), and less than $20 to do seasonal maintenance on the 2.5 Hp motor. I use the motor so little that I've done that maintenance just once, except that I always add a bit of fuel stabilizer to the motor. I also apply a persistent bug repellent once a year, but just use a tiny bit of what I use on my house, so that is negligible. I don't forsee any necessary maintenance expenditures in the next two years. So about $20/year so far. After 5 years, the maintenance costs will be $12/year.
On the other hand, I have made unnecessary improvements and upgrades to the boat, all related to performance, sailability, and launching/retrieving speed. Learning how to do boat projects was one of the reasons that I bought a small boat. They are expensive.
My advice is to make sure that the boat that you buy can be safely and enjoyably sailed without having to do any projects.
Don't forget to consider expenses such as launch fees, storage costs, club dues, taxes, licenses, etc. Also budget in a boating safety class for your first year.