Machine, no offense, but there is a lot of information on this site findable by searching, and people get tired of answering the same questions over and over again. Which is why questions like these get responses like these. There are also a lot of questions asked that are better directed to the people that do the job directly, ie Officer Recruiters. Also leads to responses like these.
I don't know the answer to your question as I drove to OCS and was reimbursed for mileage afterwards (I believe about a week into training, it was a while ago), but your son should know and if he doesn't he hasn't done his due diligence. The only reason I could see for you asking the question is if he needs money from you as the parents to get there. In that case, you either trust him or you don't.
Not trying to analyze your parenting skills or relationship issues in any way, shape or form.