Why such a high price?

[Pocus]

to have the Ai target a given individual or group of units, your only trick is to check the range of the spell, and place the mage & troops so that only they are in range.

for example :

body etheral, range 1. Put the mage adjacent to three behemots on hold an attack. Script BE 3 times. You will get the 3 beasts etheralized before they move.

Another example, weapon oh sharpness on a group of knight : I think the spell has 10 or 15 range. Place the mage and the knights in a corner, and he will have to targets them