I used a 24" bahco blade from B&Q. £3.80
They do two different bahco blades at 24", 1 tooth pattern for green wood and 1 tooth pattern for dry wood.
The wood was picked up from a local forest floor. The ropes are gardener twine. The two bolts to hold the bade were from my screw jars.
I cut the uprights at 12" and then the cross piece to fit, but approx 24". The winder was just another piece of the right sort of size.
When it's taken apart everything is 24" long and lays side by side. Just gotta make a small canvas bag for it so the blade doesn't rip up my other kit and bag.
And if anything breaks while i'm out in the woods it should be easy enough to make a replacement part from wood laying around.
So a really cheap project.