Summarize:

If you can't decide whether or not to go, try showing up for a brief amount of time. Show up for one drink or a single hour. This can work if you can't afford a full night, but want to go out. It can also work if you don't want to go out, but it's important you attend as people are expecting you. If you can't afford to go out, see if you can get people to change their plans. Instead of going to a bar, for example, invite people over to your place for drinks. Be sure to be polite when proposing this. It may be considered impolite if plans have been set for awhile. More and more people are plugged in to social media at all times. If you can't afford going out, or simply don't feel like putting in the effort, use social media to interact with others. You can video chat with a friend, make a phone call, talk to someone online, or text someone.
Try just making a brief appearance. Have people come to you. Stay in while interacting via social media.