Is this an acceptable alternative to eloping?

That sounds wonderful! You should definitely make every effort to include your family and friends. Especially now that you've alerted your guests about the date, if you decide to elope they would be very disappointed. For a group of 30 you don't have to book a banquet hall, almost any restaurant could host you in a private area I bet. That way you don't have to worry about getting out by a certain time.