Yeah seems pretty high. My old car got riddled with hail. 500+ dents. They quoted me 8000 and that included body filling, sanding, painting, a new hood, new trunk & new fenders, removing the headliner & sunroof and then pushing out all the remaining dings. This would also require removing all 4 wheels and fender liners and trunk liner as well disassbling all 4 doors.
400 for one dent seems excessive considering what I was quoted, try getting another quote. If the dent is in a fender or door could you remove the damaged panel and take it in?