Found a Colorado 10 shield for $15 a Webster, FL yesterday. A bit faded, and some dings on it, but otherwise in decent shape.
Another guy had a 36x36" PA 11 shield for $35/obo. I was unsure if the sign would fit in my trunk, so I didn't consider buying it. But in retrospect, given that it was an error shield, I should have tried...
Lastly a lady had an M-20 shield for $60. Said she paid $55 for it so the price was not negotiable. The sign was worn and she definitely got ripped off buying it. I'd have spent no more than $20 on it.