Airlines charge for a 100# minimum when shipping freight. I ordered 25# of TBS LR and a cleanup crew, two boxes total. The cost of shipping to Washington DC was ~$60. I probably could have doubled the order and still paid the same shipping cost.
It's going to vary significantly depending upon what airport you are near. TBS will try to ship it to you on the airline with the cheapest freight rates, but that of course will depend upon which airlines fly into your airport. If you talk to them they can tell you the cost to your particular airport.
I think FEDEX is the most expensive option and is usually only chosen if you are nowhere near an airport.