Your lowest prices will be renting out of and returning to the same location. I understand if there is an imbalance in cars from east to west (or visa versa) or north to south (or visa versa), these companies have trucks which transfer and equalize the cars. However, depending on each location, you might be lucky and get a car in Los Angeles, say, that belongs to Buffalo NY. They might strike a deal with you of no drop-off charges because each time they rent a Buffalo car, they owe the Buffalo outlet a fee vis-a-vis renting their own vehicle and keeping 100% of the rental. When you cross country, the renting outlet has a car at another location in which it has to split the rent. That's why the drop-off charges are what they are. Renting between LA and SF or SF and LA may not be any drop-off charges.
Again, numerous conversations with many different locations with many different companies have shown this is no longer the case. Cars are not personally "owned" anymore by hundreds of little mom-and-pop franchises that happen to fly a Hertz or Avis flag. They used to be, but no longer. This changed in the mid 1990s or so. And saying a car has to go "home," or the revenue has to be split forever, then at the same time saying that cars need to be moved by truck to meet seasonal demand, is contradictory logic. Yet these myths persist.
The cars are owned by a company that allows them to randomly circulate between corporate-operated locations. The customers usually pay to do the circulating. The rental company does not want to pay for trucks, which would negate their frequently small profit margins. Rates reflect mileage depreciation and demand, thereby creating incentives for the customers, with the goal of directing flow.
When a car leaves to a different city, the first city takes the car off its books, and the return locations adds it to theirs. The revenue is split for the one-way, but once the car is on the books of the new location, the first location no longer has much to do with it.