You will need to call your local dealers for a price.
The reason the person suggested radiator is that is the only place where coolant and tranny fluid come in close contact. The transmission fluid is sent up to the radiator to be cooled, and the person thinks you may have a split in the tube. Radiator runs under about 15 lbs, I don't know what, if any pressure your transmission fluid may be under at that location.
Before spending money, get a drain pan and loosen but don't remove the bolts on the tranny pan. Then allow fluid to drain by loosening more along one side and front and back. When the pan is nearing full or it stops draining, retighten and look at the liquid that drained. If separation is seen, determine that the second fluid is coolant to confirm their suspicions. Note: if the gasket tore, you will need to replace that also, but that is part of the normal tranny service anyway. If your fluid is contaminated with coolant, replace the radiator, and have one the tranny fluid replaced to clear the system of coolant. Only then, replace the tranny filter and the pan gasket.