Return to Launch Site (RTLS) has been the goal from day one. Yes, it's expensive in terms of payload (about 30%), but SpaceX thinks it's worth it. The cost to fill all tanks is ~$200,000, which pales in comparison to everything else. They will land every rocket they can (determined by how much ΔV the payload requires). I'm quite sure that reusable Falcon Heavy launches will be cheaper than expendable Falcon 9 launches, which incentivizes customers with payloads on the margin to choose the Heavy, which allows SpaceX to return at least 2 cores to the launch site.
(Neat little aside: launches from Florida and Texas can also take slight advantage of the earth rotating beneath the rocket in the direction they want it to.)