Maryann, you're going to run into trouble if you try to answer this question by trying to find some sort of "rule" for "who pays" in this very specific set of circumstances. Of course, there is no such rule.

The basic "rule" for "who pays" for anything is that hosts pay for the parties they host. But even that has loads of exceptions and variations; often, especially at big events like weddings, others chip in, either dollar amounts or specific items (bar, flowers, etc.).

In this case, it sounds to me like this would be an expense that the hosts of the dinner -- the groom's family, you say -- would pay. But I sure wouldn't surprise them with a bill. I would just tell them something like, "I know you are planning to host a dinner after the rehearsal, and I thought you might want to know that the church fellowship hall is available for $200, if that's where you'd like to have it."

If the problem is that you already know that they are planning to have the dinner there, and you suspect they think it's free (maybe all of you assumed so), then you will need to be very tactful. Something like, "Muriel and Jethro, I just found out that although the fellowship hall at the church is available for your dinner, they will charge $200. I'm so sorry for any confusion. Do you still want to have it there?" or whatever fits your facts.

If you have a great relationship with them, no problem, but if not, it might be easier to do this by e-mail or via the kids.

Good luck!

Great response by gellchom (as usual).

I think her suggestions are a perfect way to avoid problems with the future in-laws.