Welcome to the site. You are right to help your son prioritize getting in front of his target schools as part of his recruiting strategy.
Have you looked into Scout ball? In some areas of California, it has historically had some of the best HS talent participating and the cost with many of the organizations is very reasonable. Travel is minimal, depending on how close you are to the hub.
Beyond that, most competitive summer ball is being played via a travel organizations. Even if a given organization is not playing in front of schools that your son is targeting, he can still benefit from the competition and some of the top organizations attend the bigger national level tourneys that are played in front of a large representation of schools across all levels and all regions. Then, he can target specific schools at their prospect camps for individuals. Also, you may be surprised to know that many California travel organizations participate in events that include schools from across the country such as some of the HA events.
If you are trying to avoid the travel and costs you referred to, you should be able to find travel team options that focus more locally or regionally. But the trade-off is often level of competition.
Also, have you two researched feasibility of playing college baseball with consideration to whatever his preferred field of study is?