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The choice of camera really depends on what the user wants to see and how much they can spend.
You really don't have to worry too much about picking the exact sensor size to match the sun image diameter. There are cheap ways to scale the image.
Ordinary barlows can handle magnifying from 1.3x up. You will want this for sunspots, etc.
Ordinary reducers can do 0.9x down. Going much below f/4 is not ideal but is ok if great image quality isn't required.
The power of a barlow or reducer can be fine tuned by altering spacing.
The middle range about 1x can be done without too much difficulty. This is H-alpha, so forget chromatic aberration.
Ordinary spectacle lenses are cheap and can be finished to a suitable diameter. Anti reflection coating can be ordered. Use to make a weak barlow or reducer. The low power will not introduce much aberration.
For more money you can buy long focal length corrected doublets, negative and positive, which will work much better.
If this is for a school, as suggested in the original post, and a nice live view for a group audience is all that is needed, then high resolution may be wasted money.
The sun is 1962 seconds across, so 3s seeing ~ 654 pixel required. The display device probably will only have about 1000 pixels vertical.
If a live view isn't needed, then a 2x barlow and a red sensitive 1.6x crop DSLR will record a nice full disk image.
Observing in H-alpha is hard for many people. Maybe colour conversion is the main advantage in using a camera.
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