Then offer unlimited, right? Even if it means raising your prices, then your clients would probably like paying more knowing that pricing is predictable.

Also, I think a free trial would be nice. Just set everything up and then show it to them. Hard to say no to that.

And like patio11 recommended in one of his blog posts, write up a checklist of every feature, something that can be printed out and passed around to the decision makers.

I think you also need to make sure you're emphasizing how the site can help boost their attendance and donations and lower their administrative costs. And on that note, have you added many donation-related features? E.g., a meter to reach goals, themed donation drives, paypal/credit integration, and maybe an online merch store for church goods?