You can buy them at Macy's for $7 (I know not that much really) but why do that when you can have top performing ones for no money at all?
WARNING: This instructable involves cutting rather hard plastic with rather sharp objects. USE EXTREME CAUTION AND NEVER CUT TOWARDS YOUR HAND OR SELF. One slip of the knife can mean a deep gash, stitches, or even a chunk of your finger gone.
Step 1: Bill of Materials
A piece of plastic (I used a mayonnaise jar, number one plastic, you should find something with at least one flat spot and the plastic should not be too thick. Some milk jugs might work well if they are thin and rigid enough)
Sharpie Marker or other accessory that will write on the plastic
Pair of sharp scissors
Cutting implement to get the plastic cut into raw pieces (I used garden shears and they worked really well)
Optional--X-acto knife or other sharp precise cutting tool. I didn't use one, but if you want to achieve a high level of aesthetics, for giving as a gift, say, some find adjustments might be good
Step 2: Cut Up Plastic
Using the garden shears, cut the plastic into manageable, semi-flat pieces.
Step 3: Trace and Cut Out Stays
(If you don't have any handy, measure a square 0.9cm x 6.4cm (3/8" x 2 1/2"))
Using sharp scissors, cut out the stay along the inner edge of the marker line. Once you have the basic shape, you can trim it to the exact standards you need, i.e. some corners or smooth curves.
Now go put it in your fanciest shirt and see how good the collar looks! And don't forget to take the stays out when you wash the shirt, especially with unauthorized plastic that might hold up very poorly in the washing machine and/or dryer.
I think a pretty good test of rigidity is to hold the tabs on the edge of a table and make sounds by strumming them. The higher the sound, the more rigid and strong the tab is.
Hope this will help you look sharper around the office, in the classroom, or wherever your button-down shirts might take you, and any and all feedback is welcome and encouraged. HAPPY MAKING!!!