In article ,
says...

When I was in Maine a couple years ago the guy at the Dover fly shop
set me up with a 100 yard spool of Berkley flouro to use as my striper
leader. And you're right, it did cost about half as much as the 30
yard spools of "fly fishing" flouro tippet material.


Also, you can buy braided dacron "trolling line" in 250 yard spools
for about the same price as 50 yard spools of flyline backing, which
is suspiciously similar looking.

Kevin