Highest for me was 55-60. Two of them. One got selected for England and played one match for them, and averages 40+ in both forms. The other has played 2 OD games and 1 T20. One duck, 2 fifties at better than a run-a-ball. Both fifties not-out too.
Best bowling average when I signed a player was around 19-21, but now if I stick them there to get some form, they average 15-16.