Don't sweat the small stuff! Preschool is fun, can be educational, and is a good opportunity for socializing your child, BUT, plenty of kids do just fine without it. The key is how connected you are. First, don't just stop socializing him. Get the numbers of a few of his friends and get them together on weekends and bday parties.
Also, I don't what area you live in, but some of the libraries have some awesome story times! We live in Lincoln, and there are two that my 3 y/o daughter loves. One is specifically geared towards pre schoolers and the other is a nationwide program called Mother Goose on the Loose. They are both very interactive and tons of people go to them (we have to get there 30 mins early for the Mother Goose one or we don't get a seat!).
Make sure that you are providing him opportunities to make friends by going to the park or joining a playgroup. Those are both free options, and the way we were socialized when we were little.
Be sure that you are still providing the instruction to him at home in regards to academics. You can google your states Kindergarten requirements and base your instruction off of them. My daughter knows her entire alphabet by sight and sound, and is learning how to write, and she doesn't go to preschool, I am just diligent with her at home.
Lastly, if you still feel that preschool is important for your son there are a lot of low cost options. Some preschools are less than $200 a month! And, if that is still too much to swing most counties have a head start program that is geared for kids with low incomes who still want the preschool. A lot of people look down on these programs, but Head Start programs are awesome, too say the least. All of their teachers have more qualifications then any chain (Child Time, KinderCare, Phoenix...).
Oh, and one more option may be a preschool co-op. Use google to find all of these options, and trust me, if you choose not to put him in preschool he isn't the first child and definitely won't be the last.