Kids do not need preschool. Our parents didn't have preschool and look what their generation has been able to accomplish! Whatever your son would learn in preschool, you can do better at home since you can work/play with him one-on-one. Ever seen the test results of home-schooled kids? Anyway, look at this as a wonderful opportunity to spend time with your son. At this age, he needs you not put in a group that is expected to follow a schedule, etc.
The library is a great place to go regularly. Let him pick books he likes. Let him see how much fun reading is. Let him sit on your lap while you read to him. He wouldn't get to do that at preschool everyday! Some libraries have set story times so you can see if there are other kids he is drawn to.
Go to the parks, not just the ones in your immediate neighborhood. Even if it is raining outside, put on a raincoat, get an umbrella and stomp in the puddles! The more time you spend at parks and libraries, the greater chance you will have of meeting other moms who stay home with their kids. You can also ask around for playgroups in your area.
Do you take your son to Sunday School? That is also a nice place for kids to learn how to play with other kids.
Go for walks and explore nature. Take a magnifying glass. Even walking down your street, there are bugs to see. The more you get your son out and about, the greater chance you will see what interests him. Music, trucks, sports, animals, machines, etc. At preschool, he might not get to spend as much time on the things he likes.
Fire stations love to have kids stop by. Just call first to make sure yours is kid-welcoming.
Teach your son to be thankful for what he has. It will help him to learn how to deal with the frustrations that come along in life. I think it's wonderful that you are out of work. I hope you do too. Your son will now benefit greatly from your "mistakes"!