I discovered that United Airlines sells a great bike box for only $35. It is larger than the English ones, making it, in most cases, unnecessary to remove the front wheel. In addition, United Airlines, waves the oversize baggage fee and charges it as a checked bag ($35). However the entire package (box and contents) must not exceed 50 lbs. or an overweight fee will apply. I have used it several times with any problems.
Warning: The United Airlines bike box is 119 linear inches, at least the one we got at San Francisco International Airport was. 115 linear inches is max for United and many other airlines, as stated on the Websites.
We got a United box one at SFO and brought it home to pack for our trip to Hokkaido, Japan. I got paranoid that even if United took the box at SFO, the airline once we got to Japan, ANA, might not take it, as they also note 115 linear inches as max. So I chopped 4 inches off. Good thing I did: When we got out of customs at at Haneda Airport in Tokyo to transfer to our ANA flight to Hakodate, the friendly but legalistic staff with tape measures informed me that the box was "giri-giri," just at the edge.
United doesn't advertise its boxes online. I found out of their existence only once I called the help line to figure out what the max size was. The phone person said some airports have the boxes but that we needed to go to the airport to find out.
At SFO, the International terminal has a nice bike disassembly/assembly station that also sells bike boxes,
according to the SFO website.
Another option: Amtrak. They sell boxes for something like $20.
But as another posted, bike shops often have them for free.