I shipped some 250lb each speaker (Von Schweiker VSR) a month ago, after a lot of looking the best option i found was a moving company trucking section. i used Day and Ross (not sure if they are in the USA) it was 1/2 the cost of all the usual curriers that included insurance. the company showed up, took the speakers (in their box's) put them on a palette and tied them down and drove away. halfway across the country they arrived delivered to the door in about two weeks. total weight was just over 500lbs insurance was for $4k total from Victoria BC to Toronto (about 3500km) was $467 Canadian, take 30% off for USD comparison.
cheapest currier like UPS, Fed X was over a $1000.