美國有哪些內陸航空公司？

I take an assumption that you will fly from San Francisco, CA (SFO) to Los Angeles, CA (LAX) (with no other combination of airports like Oakland, San Jose, Burbank, Santa Ana, etc.).

The cheapest you can find is (subject to availability) is around USD$120. In most of the case, Southwest will be the most expensive choice unless you buy your ticket in less than 21 days.

You will have the following choices of airlines for non-stop direct service based on airports:

1. United

2. Delta

3. American

4. Virgin America