My guess is that if they are shipping UPS, the freight is figured on "dimensional weight". For instance, if you have a turkey body that weighs 6# in a box 24" x 24" x 18", you could be charged for 40# of freight because of the size of the box and what it "should" hold.
You might be able to charge less because you are willing to put up with the crap that the USPS provides.
I've used Greg Dorrance Co and have been super impressed with their customer service/speed.. I know they have a bunch of stuff Van Dykes has, but it just depends on what exactly your looking for? May be worth checking em out