The nursing home where my grandmother lives actually has a pretty swanky menu. They do a 4 week rotation, so a total of 32 different lunch and 32 different dinner options.
A lot of the things I saw were items that easily can be made for bulk but still cheap. For example lasagne, shepard's pie, meatloaf, and roast chicken. This way you're not buying 35 chicken breasts and having each guest get one.
That's definitely my suggestion, try to have as many meals as possible be "family style" if you get my meaning. There were only a few individual things on her menu such as chicken fried steak, hamburgers, poached fish, i.e. things that you have to purchase one of per person.
Hope it helps, and thanks for trying to bring quality food to the older generation. It always makes me sad when they get forgotten.