The degree to which they are a rip off is proportionate to your own travel costs. For example, even though it is more expensive for me to do a one way rental from St. Louis to Kansas City, it is cheaper than making two trips..two flights, two cars. I still have to cover both cities either way and if I land in one I am not going back to it just to catch my flight home and return the car.

There are expenses incurred by the rental companies for one ways, including on the state taxes, emisions, inventory control side. Like everything else you just have to run the numbers to see if it's still cheaper for you across all accounts rather than in comparison to a standard rental.