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If nobody has a specific use, then maybe between $0.01 and $1.00 per #.
If you can make use of the items, then for your purpose you have to make a judgement call. If no one else is bidding, then use the scrap metal price.
If nothing else is done with the PLCs they should go to schools or kids for learning about the devices.
After WWII we spent a lot of time at surplus stores getting various items. One was an aircraft transmitter with an 832 output tube that was close to the 2 meter band and easily converter for use there. I bought a 5BP1 CRT tube and turned it into a semi-useful oscilloscope. Aluminum was not a common material at that time and we got tubing to use for antennas. Lots of other interesting things to look thru.
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