If you don't need miror lockup and detatchable finders, I find the FM3A to be a great backup to my F2AS. Its all mechanical but can work with batteries to (hybrid shutter). It will likely cost you more but it is almost brand new compared to 30 year old F2AS.
That being said, I am almost always picking up my F2AS. There is something about the mirror "kerlunk" that just makes me feel like I am taking a better picture.
Lastly, another option is an Olympus OM-3Ti, a fully mechanical camera with great lenses and a nice spot metering option.