My friend and I needed towing mirrors for his 93 diesel f250, and we decided that we should make them at home using scrap metal. For us this project was free. If you had to buy the parts it would probably come out to around $15 the angle piece of aluminum was about $13 and then some misc. hardware.

Step 1: Parts and Tools

2x Desired length of 1" angled aluminum
2x 1" long bolt
2x nut
2x locking washer
C clamp
T40 torx bit
other sockets to fit the bolts you get

Step 2: Prep

remove the existing mirrors, this is where you will need the t40 bit. save the mirrors because you will be using them in a few steps.
Cut the aluminum to the desired length, for ours we wanted the mirrors to stick out 10", and then we needed a bit extra to clamp and secure it to the existing mirror bracket. it ends up being an extra 4 inches of metal to the needed length to get it sturdy.
Drill the holes, the one used for mounting to the bracket should be 4" from one end, and the one that the mirror attaches to should be about 1" from the other end of the aluminum

Step 3: Assembly

Attach the metal extensions with the bolts
add the C clamps at the short end of the extension to make it more secure to the truck
attach the mirror to the second hole
you are good to go tow!