My fiancee and I are having a hard time picking out a venue because we don't know what we will be able to afford without knowing how many guests to expect. We can afford a very basic wedding on our current budget if everyone on or guest list comes, but we can go extravagent if only 1/2 the people come. With so many guests being out of town that is a real possibility. Is it okay to send out a kind of "Save the date card" that lists the city and date information and then say a formal invitation with the address will be sent after RSVP's are received? Or is that not considered polite?