I have shipped two boats via DHL, one from Florida to New Hampshire and the other from Florida to Tennessee. Both cost me about $60. The key is to arrange for a pickup at your residence, versus taking it to a depot, because the driver could care less if the weicht and dimensions are exactly right. This gives you the ability to "fudge" a little on size and weight in order to get a good price for the shipment. Also, you will need a computer printer to print out your airbill, and something clear and plastic, like a page sleeve, to put the airbill into and tape onto the kayak to make sure it doesn't fall off and the boat get lost in transit.
To pack the boat, get one of those brown/silver garden tarps at Home Depot or Lowes, with the diagonal about 2 feet longer than then length of the boat. Lay out the tarp, brown side up, and place the kayak on it, with the bow and stern diagonally. Fold the corners back, onto the bow and stern, and affixe with silver duct tape. Then fold in the side corners to the side edges of the kayak then fold up the rest of the sides, across the cockpit coaming, and secure with silver duct tape. Finally, make about 6-8 wraparounds, starting at the bow and stern, to secure the folded tarp. It will end up looking like a silver mummy!
As for insurance, one of my boats arrived in perfect condition, but the other one, the buyer said there was a scratch on the hull from shipment. I don't understand, because in order for that to happen, the tarp would have been damaged, and he said it was not.
If I was going to ship a kayak again, and I am sure I will, I wouldn't hesitate to use DHL, door-to-door.