Welcome Get Together (post Reception)

We're thinking of putting something together (informal) for after the rehearsal dinner since we will have some family/friends in town. We are already spending a ton on the wedding so were thinking of doing something more casual like "We're going to be at X bar from 9-11... feel free to stop by and grab a drink with us." Is this tacky if we don't pay for drinks? What's the best way to organize that and word it to not sound tacky? We are just thinking it would be fun to see some of our out of towners.