QUESTION: Why does my multicity booking seem so much more expensive than it used to?
ANSWER: Recent online booking tool changes from American, Delta and United Airlines may not display the cheapest available fare for each leg of a multicity round trip (e.g., Los Angeles to New York; New York to Orlando; Orlando back to Los Angeles.) But you can save big with a little extra legwork.
Before you purchase any multicity round trip, use a third-party booking site like Kayak that lets you compare airlines. You can also check the one-way (not round-trip) fares for each leg with multiple airlines. This works because big airlines often discount one-way travel in an effort to remain competitive with discount airlines like Southwest, which specialize in those fares.
Source: Bottom Line