My chapter of Alpha Phi Omega was Omega Mu (right when Revenge of the Nerds came out) so I feel your pain.
One year a lot of our sisters couldn't attend a Christmas semiformal for one reason or another, we only had about 16 who could go, so the people who were going got dressed up and went to dinner at the nicest restaurant in town and then we had a small party at our house. You might want to do something similar rather than fussing with a DJ and such. It was actually a really nice classy evening.