I have to say in my own experience, preschool was invaluable, even if it is just a few days a week or half days. Interacting with other kids at a park or library with mommy right there is just NOT the same as learning to play independently without a parent right there.
Going to kindergarten and leaving mommy for the first time for this strange new 'school' atmosphere is going to be much harder for your child if he hasn't had any practice with it in preschool. Also, it is likely that most of the other kids there will have had some preschool, so you don't want your kid to start out being the kid who is crying and screaming and hanging on your leg because he hasn't done this before. That kind of thing will happen- but it is less common in kindergarten, just because most kids get it over with in preschool first if they are going to be that upset. Think about how your child adjusts now to social situations and how this could make kindergarten more difficult for him.
My son was in a small home daycare/preschool run by a former Montessori teacher and her husband. There were 6-8 kids there, ranging from age 3 to 5 and 2 kids who came afterschool from grade school. As an only child, my son really benefited from being around kids who were both bigger and smaller than he was, and learning he was NOT the center of attention all the time!
He is almost 11 now and people often remark on how patient he is with younger children- I am absolutely sure it is because of that early preschool experience.
But preschool was great not just to learn ABCs and counting and colors etc (schools expect a LOT more of that right in kindergarten now than they used to) but because it taught processes- to line up when you're told, wait your turn, wash your hands, hang your coat on the hook, don't push while you're getting into the van, find your partner, stay with your partner, etc.
There are just some things kids need to learn to do in a group and the earlier they learn, the easier it will be for them to adjust to school. I had a wonderful caregiver and honestly never worried for a moment when my son was in their care. If you can afford it at all, find a good daycare/preschool you like and feel comfortable with and have your son go just a couple of times a week or for half days. I think it will really help prepare him in the long run. good luck!