Did you realise that some of the major tool companies want over $50 au for a simple aluminium straightedge?
I made my own for about $8 by getting a piece of straight aluminium from the local hardware store and putting a hang-hole in it and it works great.
First, mark a cross on one end. Using the 45 degree angle on a combination square will do the job just fine, or you can use a centre finder if you happen to have one around. Then use an awl to mark the centrepoint.
To make it even easier to drill, use a centrepunch to enlarge the point you marked with the awl
Clamp the straightedge to the bench and drill the hole.
Then just to make it look more finished, use a countersink bit to chamfer the edges of the new hole on both sides
There we go, all done. It’s perfectly straight and took all of 15 minutes work!