I got a transmission shipped to me from New York to Texas via FedEx Freight for $175. Of course, the tranny fit on a pallet and that made all the difference.
I work for FedEx and although I get discounts for Express shipping, there is none for me with regards to freight. So that was a typical customer quote for the tranny.
Unfortunately, you are dealing with what we cal in our business, "Dim Weight" or dimensional weighting. In layman's terms, we have to charge not just for weight, but also for the space it occupies. If you were a distribution center, your shipping would be lower overall because you can cram a bunch of smaller items along with your body kit, and the total would fit inside a shipping container. But your only shipment is the body kit, and you are being charge for the amount of room it would take inside a plane or truck.
Unfortunately, unless you might find a small-scale carrier to accomodate, you are probably going to get the same answers from the big three (UPS, FedEx, and DHL).
I ran into the same problem with trying to get a rocking chair shipped...shipping costs exceeded the value of the rocker!!