is a 28 inch suit case allowed on the plane, not as a carry on?

My ticket info stated that United & American charge $30 to check the 1st 50 lb bag & $40 to check the 2nd 50 lb bag. Wish it were still free! Does anyone know if that’s what they charge for all bags UP TO 50 lbs?

Yes it is

To check it in should be fine

My 24 inch was too big, so I would say no

Depending on the width of your bag, you may be forced to check it. Most airline check-in booths provide a kiosk which you can use to see. If the bag does not fit within that kiosk, you will need to check it. It will cost you to do so.

No sure