The easiest (and cheapest) way to tie the knot with strapping is using a buckle.  Companies like Allstrap stock all kinds of buckles.  If you need non-metallic you can use a plastic buckle (for 1/2″) .

The standard wire buckle is metal wire that is bent to look like a pretzel (top in lower pic)

The most unusual buckle is a one leg up, one leg down (bottom in lower pic).