I agree about the price of these things - it seems way too much.
You could probably go to your nearest leather hobby place (Tandy, etc.) and pick up some remnants of chap leather or something similar for $5-$10 and make your own boots. It would be dead easy to make a pattern out of cloth then transfer it to leather and sew it up with some waxed twine.
Or try a consignment shop like Second Wave in Seattle:
http://www.secondwave.cc/
Last time I was there they had a ton of used junk - boxes and bins and trays - and it's possible there are some old spreader boots there. Call them - their store has much more stuff than the website would suggest.
Carlos