I personally use 100ft. Most 40 and 60 sized planes can recover in the distance without to much of a problem but you will need to be quick on the sticks.

The type of manuver also dictates how high you need to be.

When I first started out I was always 200 - 300 feet high. Now I'm hovering at 20 feet and slowly creeping down although I admit my hovering needs allot to be desired