Doing a little checking: a used 70-200 F4 L in decent condition can be had for around $600. While it's certainly possible that a repair would be $300, it probably won't be that much. The Canon EF 70-200mm f/2.8L IS USM is a high-performance. Lens surface and internal parts. Manual focusing enabled during AF. 70 – 200 mm, f/2.8.
Official Certified Canon EOS and EF Service and Repair Manuals can be found now and then using Google. As a Canon camera owner, it is fairly crucial to keep a Canon EOS service & repair manual available at home. A lot of people today can perform basic repairs on their camera.
Without a proper service & repair manual though, this may be a particularly challenging task, even for more advanced users. For owners not ready to do the repair themselves it is both interesting and very good to know more about the repair even if the camera is brought to a professional repair center. Don’t worry about unnecessary costs as you know more about the inner workings of your equipment before you talk to the service center. In many cases it is possible to do the repair yourself but it is crucial to have accurate and complete information for your camera. Since the manual is created by Canon you won’t find a better source anywhere else.
Do not count on too many step-by-step instructions. It is normally only a schematic with part numbers for each piece. Still this is invaluable information when ordering pieces and trying do dismount the equipment.
Because the manuals are copyrighted by Canon it is impossible to make a download available here, instead use Google or other sources to find them, here are some examples of how the official documents are named. Canon Lens EF 50mm 1:1.4 USM Parts Catalog Canon Lens EF 35mm 1:2.0 Parts Catalog Canon Lens Fish-Eye EF 15mm 1:2.8 Parts Catalog Canon Lens EF 70-200mm 1:2.8L IS USM Parts Catalog Canon TS-E 45mm 1:2.8 Parts Catalog Canon EOS-1D Parts Catalog Canon EOS 5D Parts Catalog.