That depends greatly on the part number. I am by no means an expert in this area so others should mention any notable ones that I miss, but here they are from least to most rare. All my estimates assume the unit is in pretty good condition:
Black Oval Badge Models (1394946, 1394950): ~$150-200
1394946 is probably the most common Industrial Model M variant out there, so it is naturally going to be the cheapest. 1394950 is a bit less common to my knowledge but they came out later (generally less desirable for a Model M) and don't have an embossed badge, so I'd say that puts it on the same tier as 1394946. There was a 1394946 that sold for just under $200 shipped two months ago, and I myself nabbed a 1394950 for $170 shipped (just a few dollars above the next lowest bidder) just a few days ago, so I feel the most confident about this particular price estimate.
1390653: ~$250-$300
These are the the most common square badge industrial, but the badges can be silver or black. According to some older posts on these forums the silver badge versions of these are actually rarer. I am a bit less confident about this price estimate, but the most recent one I saw sold for around $275 shipped (but still not very recent). They generally don't turn up for sale that often, but I have been looking for one of these for a little while now.
1388032: ~$500-600+ ???
Probably among the rarest Industrial variants out there, these are also some of the first Model M keyboards ever made (dubbed 0th generation in Chyros's Model M video). As such they command a considerable premium over just about every other full-sized Industrial (Industrial SSK's can go for $1000+). There was another closely related and rarer variant (1388081) that has a silver badge, which Ellipse is currently selling for $800.
Hope that helps, I would also be interested if anyone here has some more recent sales data for the square badge industrial variants that I haven't seen.
