If you were not a member of church and just "using" the church and minister for wedding, do you invite minister and wife to these dinners? And would you expect a gift?

If you send the minister and his wife an invitation, they may feel obligated to give a gift of some type. Therefore, if you want to invite them to the rehearsal dinner and/or the reception, you might do so verbally so that they know that there is no obligation on their part to give a gift; rather, you would enjoy their presence. Just be sure to invite them several days before the rehearsal, not at the last minute. When an invitation is extended at the last minute, it gives the impression that he/they is/are an after thought. When I am invited to the rehearsal dinner under those circumstances, I decline (I'm a wedding coordinator).

If the minister has spent several weeks with you doing counseling, he may choose to attend the reception for a short time, but I find that most ministers leave after about 15 or 20 minutes. They don't want to appear to be rushing off, but they are not really interested in staying for the entire evening when they don't know anyone. If the reception is not being held at the same location as the ceremony, he may choose not to make the drive to another location for a brief appearance.

You don't need to invite the officiant to the rehearsal dinner, but you really should invite him and his wife to the reception, and yes, you do it by sending them a regular invitation. Otherwise, you are sending the message that he is not a social equal, just hired help or a vendor. But you say he is the minister at your parents' church, not some freelancer (in which case I would not feel you had to invite him). As I said above, the custom may be different in your parents' church. But if it is the custom to invite clergy, then it is very rude and disrespectful not to do so.

Whatever the local custom, the following factors are completely irrelevant:
- how often your parents attend church
- how well you personally know (or like) this guy
- how much your reception costs per person
- how big of a gift you estimate you can expect to cash in on from him

And now I will give you the good news. It seems that your concern here is that this guy (and his wife) will be expensive to include, and might not come across with a gift big enough offset that expense. Well, guess what: they probably won't come anyway, because, as you said, they don't know you at all and evidently aren't close with your parents, either. Your parents will know if he accepts every invitation, but I'll bet you he doesn't.

As for your questions,
"Do you expect to get a gift from the minister? What kind of gift or price range?"
I'll just answer, not comment: we give a gift if we attend, and we give the kind of gift, in the kind of price range, we would give if we were any other guests. If you are applying some sort of what-can-we-expect-them-to-fork-over formula to your relatives and friends, just apply it to the minister, too.

Sweet Pea, I wouldn't do an oral invitation. Clergy know they are not obligated to send a gift every time they receive an invitation (we get several every week), just when they attend (or can't attend, if it's the event of a close friend that we would have gone to otherwise). So I don't think that it is important to avoid a written invitation in order not to make clergy feel obligated to send a gift. Conversely, I do feel that an oh-by-the-way spoken invitation is kind of a snub -- "A list" guests certainly don't get those -- and sends at message that the hosts really don't want the person there (at least in the case of an invitation to the wedding reception, not so much for a rehearsal dinner, if they decide to invite him to that -- I wouldn't think that that requires a written invitation).