Preschool programs are generally for children ages 2- 5, whereas kindergarten is for children who are usually age 5 when they begin (for public schools, the youngest they can be is 5 by Dec. 2 of the year they begin kindergarten). Daycare programs are generally available during normal parent working hours, for example, 7 am to 5 pm or 6 pm Monday - Friday. Daycare often includes a preschool program for children in the preschool years of 2 or 3 to 5, but there may be more free play time and nap time that would not be part of a strictly preschool program.
Because of your son's age and the hours of school time you are seeking, yes, preschool would be the best setting for you. What a child learns in preschool depends on the school's approach. There are many good preschools in Mountain View, including Montecito, St. Timothy's, Little Acorn School. Though the fall sessions begin in August or September, most people register several months ahead, so now would be a good time to ask to visit several of them to find out specifically what each offers and how your child would fit in and benefit.
Two of my sons attended Little Acorn, which has a preschool program as part of its daycare program. At the time they went, there was an option to take part in a Spanish program (at a small extra cost); I don't know if it is still offered. This is a Christian program with a grace before snacks and occasional pastor visits. We also visited Montecito and loved the setting with farm animals, as well as the many varied activities we saw the day of our visit (crafts, movement with parachute, etc) (we did not enroll because of the schedule). St. Timothy's also had an excellent program, with a well-regarded science program for 4-year-olds.
For the costs, you'll need to inquire with the schools, as I don't have anyone there currently. At the time I was inquiring, all of these three schools I mentioned were reasonably or competitively priced.
One of the main non-academic benefits of preschool is that your son sees same-age peers regularly. This can lead to friendships and the ability to give and take with others.