That's a good question Iamvintage. This SG copy certainly has some attractive selling points but also has features that really undermine value in my mind.
As pointed out by others on this thread, it appears to be a clean, unmolested example of this model. The "Ry Cooder" gold-foil pups are another attractive feature. I've seen these pups sell as high as $75 apiece on the bay.
To me, the biggest drag on value is the hardware. The fact that you cannot adjust intonation with that bridge is a huge issue if you want to use the guitar as a recording tool. Of course, I have a load of guitars with a bridge like this and occasionally one will have intonation that is pretty close, but that's the exception. If there is an intonation problem, the best you can do is try to find a bridge that is adjustable and will fit the existing posts.
Those tuners are iffy. Sometimes I've had tuners like these that stay in tune remarkably well, but more often, they are worn and tend to slip.
I guess my last issue is with early Korean production. Once builders moved production to Korea, it took a few years to get production standards up to snuff. Given that this is a fairly early Korean model, I'd want to give it a good look to check fit, alignment, etc.
I did a quick search of the bay to see if any similar examples have sold recently. I didn't find anything that I believe is really comparable, this fella with the changed tailpiece was as close as I could find. It sold for $99:
In another thread posted this morning, Big Beat makes the point that in 70's Korean guitars with DiMarzio's installed, the pickups are worth more than the guitar.
I think that could easily be the case here. I'd be surprised to see an SG like this sell for much over $200 which seems crazy when you potentially have $150 worth of pups on board. But, as is the case with many Teisco's, the parts sold seperately have more value than intact guitars.
Of course, I ask that you please keep this instrument together