i'm sure Deere has a patent on their decals and the designs of them, so if there were somewhere else you could get them for cheaper, they wouldn't look the same as the ones you had.
Most sign shops that make the vinyl stick on signs use a computer to make them. Our sheriff's office has theirs made that way. I needed a Dodge 4X4 decal for my tailgate. The guy told me to take a picture of one somewhere with a ruler under the decal and he could make it. It cost me about 1/4 th what Dodge wanted.
Also, contact Ken Kastner at K&K Tractors located in Shelbyville Indiana for some of the finest reproduction JD decals I've ever had the pleasure of using.