Wedding Invitations - Cash Bar

My venue offers various options for bar service. One option is we get the bill at the end of the night (which could be a surprise and potentially a lot); we purchase a package of beer, wine, and liquor if we choose and pay for every guest over 21; or we set a dollar amount that we want to spend and after that it's a cash bar.

We're leaning more towards the last option that way we won't be left with any surprises at the end of the night. Plus, a lot of family aren't big drinkers. That being said would you include that in your invitation or on your wedding website somewhere? I feel like we should somehow let our guests know that they could potentially have to pay for their drinks. We can't really say cash bar after this time because who knows when our limit will be reached.

Should I let guests know at all?? I would think they would want a heads up so they know to bring cash