Their policy is a bit confusing. They in practice do not limit you to 80", if they did no regular bike could fly with them. The language in the bike section of their policy does not list the size limit for boxed bikes at the $50 charge. The regular baggage section of their policy does say that the limit is 80", but I know that many people have flown with boxes of over that size. I spoke with them before my June 2010 tour and was told that a box over 80" would be fine. I was still nervous so I asked on a couple forums and heard from quite a few people who flew on SW with boxes like bikes come in when new with no problem and heard from no one who was turned away.

I think it prudent to not go crazy and use a huge box like the Amtrak one. It seems to me as if that would be asking for trouble.

On the coupled bikes with a hard case, I don't think they would work for me because I do not typically start and end my tour in the same city. Because of that I would have to figure out how to get my case from the start of my tour to the end. That would seem to me to defeat the whole purpose of having a coupled bike.

If on the other hand you typically fly to a city with your bike and fly home from the same city it may work out better. Also I guess you could use a cardboard box the correct size for the coupled bike, but again getting the right box seems like a big complication at the end of a tour.

On the building up vs buying a complete bike, I bet most find they wind up spending MUCH more building one up. I find the component selection on most complete touring bikes to be quite good and the bikes a good enough value that it seldom pays to build up your own unless you just want to do it and are willing to spend more doing it.

Some people do manage to build up a bike cheaper than buying complete by buying a piece here and there on deep discount or used on eBay. They are the rare exception. They also probably spend a long time collecting the parts