It's a great question. Socializing with your friends is important. Isolating yourself to save money would be counterproductive. Therefore, since you are the one in your circle least likely to attend, it's important to consider more frugal alternatives and being the source of them.
For example, you could suggest a cookout instead, or even better, before that invitation arrives. A lot less money and just as much fun (and you don't have to give up the table either!). During dinner you can casually point out how much cheaper the steaks and beer are, and gosh, why don't we do this more often? :)
I do appreciate all of the honesty is the best policy comments above, I've considered similar things recently as I know I am going down a path that is different from many of my friends. They aren't consciously setting fire to their twenties, it's just the cultural norm and I am moving outside of the cultural norm. I have great friends, and since I am the one changing my lifestyle I feel like it is on me to offer good alternatives.