Help!, 300 2.8 fEE error
Sometimes with a lens this large we can get a touch lazy and not turn it until the lock button "clicks" in place. If you "short mount" a lens on the D70, it's almost guaranteed you'll get the FEE error.
The second thing to look for is wheter the minimum aperture signal lever is being shifted by the lug on the aperture ring. The signal lever is at 7:00 by the lens mount as you face the body. Your lens may have had this lug broken off and that would cause a FEE error because the lens can't signal the camera that it's set to the minimum aperture. If that's the problem, a new aperture ring shouldn't cost more than 50 USD but you may have to wait a few weeks for shipping. It the lug is present, and is moving the lever on the camera, then it's an electronic problem and I have no idea what a repair would cost.
BTW, if you can lay your hands on an older Nikon AF body, you can test the communications between the lens and the camera. The bodies you want to use are the ones up to the N90s, specifically, N2020, N4000, N8008s, N90s, F4, or F5. These cameras don't use a minimum aperture signal lever and get their confirmation electronically from the lens. The later film bodies like the N80 use the signal lever method.