From what I understand, the NEWEST billet intermediates cost less than $800, and will out last the stock shaft.
I have a truck with little power and broke a stock intermediate. So, when I was talking to the trans builder, a billet intermediate was one of the more important topics that we discussed. Like you, I had read that the stock intermediates were holding up just as well as the billet products available. When I asked the trans builder, he told me the NEWER (not sure how far that goes back) billet intermediates aren't breaking....yet. Which was confirmed by a seperate trans builder on the opposite side of the country.
If you are already breaking stock shafts, why not atleast give the billet a shot? I could have thrown a stock shaft back in the truck and saved $600, but I decided to trust the reputable trans builder instead.