Unfortunately, while many museums in Los Angeles are free on the first Tuesday or Thursday of the month, that does not apply in July and August, which is prime tourist time. There are a few that will still have free days, but they tend to be art museums {not on your list) or have expensive on-site parking. The same goes for beaches. Even though the area between Los Angeles and San Diego has a lot of coastline, much of it is increasable due to terrain, private homes, or being part of a military installation. What beaches there are usually crowded due to the high population density. Many of them have 'demand pricing' meaning they'll be especially costly over the July 4th holiday.
Las Tunas Beach, north of LA is one possibility.
Your best 'scenery' will be inland, including such sites as
Joshua Tree National Park but check the Elk Fire status before going, the
Santa Rosa and San Jacinto Mountains National Monument, and
Anza-Borrego Desert State Park.
Mojave National Preserve is on your route between LV and LA, but even though a couple of its visitor centers are closed the roads through are open and it's free.
As for accommodations, when I'm traveling alone, I like to stay at lower cost but well-known chains such as Days Inn, Microtel, America’s Best Value Inn,
etc. If you belong to a loyalty program, now might be the time to use and/or earn some points. If I'm going to be out most of the day, I just don't see the point in spending a lot of money on a room that I just sleep in. the advantage of going with a nationwide brand is that there is someone to complain to other than just the local franchise.
Hopefully, others will respond with more or better info,
AZBuck