1866Yellowboy - Having purchased several components from Mar-K , I found your post interesting and went to their website to review. Your determination that the fenders are not made in the USA is correct, they are imported, per the website. I also researched the varying prices from different vendors, and yep, a lot of variation :
Jim Carter - 460.00
LMC - 385.00
Classic Parts - 595.00
Chev's of the 40's -475.00
The Filling Station - 425.00
Mar-K - 576.00
I think I would do the cost of shipping comparison you mentioned . You may find that wrapping the shipping costs together with the other items you planned to purchase may be the most cost conscience approach. Regarding the quality, I think that Mar-K would not put their stamp of approval on any product that was of marginal quality. As an alternative, you could consider searching for used fenders starting with a parts wanted listing within the Parts Wanted section of the swap meet.
Would like to hear the outcome, including what you learn from 59Fleet. Good hunting!