I bought 4000 ft of 5 mm diameter "dyneema" from the Shanghai Tough Rope and Webbing Company back in 2016 and we have been using it on our winch for 2 years.

http://www.toughrope.com/productshow_261.html

I tested it on the tensile machine at my college and it reached 3800 lbs before breaking. Lower than expected, but I had not mounted it very well in the machine and it was cut, more than it was broken, and 3800 is well above the 2200 lb weak link required for the K-21 so I didn't bother to mount it better and test it again.

Price in 2016 was $0.50 per meter and $200 in shipping. Much cheaper than Amsteel for pretty much the same thing.