Ok, if all interest is in cost, you can make your own straight edge from a piece of meranti timber.
As long as you want it, around 3" x 1" profile, chamfer it down on one long edge and sand nice and smooth for the cutter to run along.
I cut with one of these for a couple of years when I started doing glass work.
Mark measurement top and bottom of glass, line up straight edge with cutter offset to marks, cut glass.
The point of using a braced square in hand cutting is that you can save a LOT of measuring time, mistakes in measuring 2 points and alignment, mistakes when the a straight edge moves on you slightly as you score.
Only when I did a framing show here did I invest in a speed cutter (used for 1/8" and thicker glass) and braced squares . . . I have around 500 pieces of glass to cut and convex).
Boy, those tools paid for themselves 100 times over, just from that event, and I wondered why I ever bothered to do things the hard way for so long.
Les