Just my two cents, here. But, based on the priests I know and their personalities, I think a gift that's not a gift is the best. What I mean is something he is able to use to help others or help his spiritual life (such as icons, etc.). What I mean, is like the incense or the restaurant gift card, where his presvytera could go with him. I especially like that idea because I think, all too often, we overlook the presvytera and how important and hard her job is.