I'd recommend staying at the Ocean Beach Hostel--that's very convenient to the start point: https://www.hiusa.org/hostels/califo...ego/point-loma

If you really really want an inexpensive legal campsite, you could take the Coaster commuter train up to Solano Beach, ride a couple miles north to the $10 hike and bike sites at San Elijo State Beach, then start the trip from there the next morning. You can head inland to the I15 corridor, take that south to just south of Hwy 52, then follow that to Santee to rejoin the ACA route at Mast Blvd.. There is also a city campground directly on the ACA route about 15 miles east of the starting point, but it's only open for camping Friday and Saturday night, though a resourceful cyclist could find a place to stealth camp in the nearby brush--it's too far from services and public transportation for you to encounter homeless issues. But my druthers would be the hostel or San Elijo: https://mtrp.org/campground/