Here's a link to a prior thread on new 3 bottom plows:
http://www.tractorbynet.com/forums/attachments/203012-new-3-bottom-plow-who.html
The gist of the story is that John Deere ($7500), Kverneland (over $10,000), and Kuhn ($9500) all make new 3 bottom plows. Also a company called Overum.
Now do you see why everyone buys used?
1. Farmers who still plow are high acreage, high horsepower farmers and buy much bigger plows if they buy them at all.
2. Farmers who still use 3 bottoms can't afford and don't need the new ones because their acreage is so much smaller and there are so many used ones on the market.
You can buy all the replaceable wear parts you need for most used plows out there and only spend a couple hundred more. Even if you were to sandblast and paint a used one, you'd be into it for like $1500 and have a plow as good as any new one out there.
I will say, if you are questioning the high cost compared to a King Kutter or Everything Attachments 2 bottom model, just look at the pics to compare the construction. The big dollar plows all have massive box beam construction, not flat plate bolted together. They are made to do hundreds of acres a year and last for many years. The others simply will not hold up to that kind of duty. They are low cost point solutions for the backyard hobby farmer and not meant for a large or commercial operation. The demand just isn't there.