Worth at least $250, I would say as high as $325, more if bolt-modded.
I don't think it's bolt modded. I've got this from a guy who was selling his old stuff.
Do not bolt-mod it.
First, you seldom get any extra money, and very very rarely enough to make it worth all the time and trouble.
Second, if you hope to get a premium for this, it will be from a silly collector who will want it "factory stock" without any modifications at all.
If I had this keyboard, I would clean it and test it thoroughly, to ensure that it was immaculate throughout, and then list it at a ridiculous high price.
I would probably even drop $40 on an orihalcon cable to make it even more desirable.
Then I would lower my price by 10% per week until it sold. If it sold in under 24 hours, I would kick myself for pricing it too low.