Your cheapest way is to remove your glass, take it to a local glass company and have them cut a set for you. Be sure to tell them that you DO NOT want any glass company logos on the glass, just plain glass. Then, contact Roy Nacewicz and buy a set of his Ford Logos (Bugs) for the correct year of your car. You would only need to take the glass from one side of the vehicle as both sides are the same, you just need to put the Bugs in the right place. On one side the Bug will be on the inside, and on the other side the bug will be on the outside. I am sure Roy has detailed instructions on how to position and apply the bugs. If you have any original bugs on the windows you should note the date on the bug and order the exact same bug.
If you are a strict purist, you will need glass with the black edge on the laminate between the two sheets of glass, but then that is where you are getting into mega bucks. I believe in 40 they still had the black edge on the glass. Sanders I believe it is can do the black edge and the bugs but to be honest with you, I don't think it is worth the difference in cost. If the judges notice no black edge they will probably gigg you a point or two.