How much does it cost to deal with something stripped the bark off my young tree?

This is usually not a tree service call at all, and an honest company will say so. Removing a girdled sapling sits at the small end of the price list and often lands on a minimum-charge visit, and the stump is small enough that grinding may not justify mobilizing a machine — it can frequently just be dug out. The genuine spend is replacement plus protection: the new tree, and guards or fencing on everything young in the yard. If several trees in one planting were hit, ask for the whole group to be looked at in a single visit rather than paying a trip charge per tree.