How Do I Ask A Minister To Marry Us?

I was raised Catholic, but don`t practice anymore, and my fiance wasn`t raised with much of a religious upbringing at all. We don`t want to get married in the church (and are planning a relatively informal outdoor wedding, which rules out Catholic priests from doing the ceremony). I have been given several local ministers` names as possible people to do the ceremony, and I think I`d like to ask one of them to marry us (she is Episcopalian). How do I go about doing this? Do I just call her up and say "Are you available to marry us?" or is there some more tactful way to go about this? And does it matter that I`ve never been to her church?