How expensive is plane travel in the US compared to the EU? The language won't change, but the variety of the US is pretty immense. You could hop on a plane from LA and be in the Texas desert, or the peaks and snow in Colorado, or the Great Lakes, or the swamps in the South. And even leaving the States, tropical islands of the Bahamas are only 5 hours away, Canada is three or four, and Mexico is even closer. I would have expected air travel to be cheaper relatively speaking in America than Europe, especially with the higher salaries. The environmental impacts of all the flying aren't great though obviously.
Where budget airlines exist in the US the fares are comparable, they just fly far fewer routes than in Europe so you often end up paying standard airline prices.
The variety of the US is immense, but its size is immense too! San Francisco-New York is three quarters the distance of London-New York and the western half of the US is practically empty other than the coast.
Looking at my old email receipts I have a lot of £50 each way tickets from RyanAir and EasyJet. My last trip to Mexico was $200 each way (though that was at least twice the distance, Mexico is huge too!)
