The person I asked to be my officiant was the Pastor at the church I attended growing up. I just asked him over Facebook (terrible etiquette, I know, but I don't believe he currently is leading a church so I didn't know how else to contact him besides FBing him or his wife.)
He said "of course!" and that he just needed to know date, time, location and he'll be there. If he doesn't mention a fee or pre-marriage counseling, should I ask? It feels tacky to ask about money.
(I should add that with or without a fee, I was going to make a "donation" or "tip" to him out of appreciation. whichever term you want to call it...)