This is such a rare post on CC because parents are usually in a position of imparting the bad news to their student that they can’t attend a more expensive school. It’s sort of refreshing that the LAC is less expensive! But I certainly see how challenging this is.
The impact of an ASD kid bonding with a future classmate with a shared interest cannot be overstated. Your son foresees that he will be happy at the LAC and he likely will, and it will be his own decision. If he ends up miserable, he can transfer, you can be “right” and it’s not the end of the world. If he chooses the larger, closer university and he ends up miserable, it will be on you. And I would guess that the full ride offer at the LAC will go away.
I don’t know which schools you’re considering here, but IMO the larger the school, the more likely an ASD kid will get “lost” and be lonely.