They're only worth what someone will give.
It depends on wear. If the heel thickness is 10% less than the vertical thickness, they are considered worn and according to OSHA are scrap. Enough with the lawyer talk. I used to sell used pairs 42" long and longer to my local farmers for $50 a pair. These were also 4" wide, yours are wider but shorter. I'm also told I could have gotten more, but I have a soft spot in my heart for farmers.
Treemonkey, contact a local forklift repair outfit and tell them you need a set that are worn out. Better yet, go there with a box of donuts and some cash. Instant friends.