Wow, this thread just took a turn for the painful, thanks to NES Gansta. It sort of reminds me of when you see that old, high school friend of yours about to make a bad move, like marrying a girl on the rebound that has children with a different father. You just cringe, and wish that somehow you could help your buddy out, but at the end of the day, they aren't hearing it and you can say / do so much without looking like the bad guy. That is how I feel with this situation.
NES Gansta could have upped his bounty even more, to get a copy of DKJR Math box to his standards. Like others have mentioned on here, I know how it is to be in one of these situations. I have some rares that I will not trade / sell, unless I get a good offer. Going rate sometimes isn't enough, if the seller enjoys the item themselves...sometimes you need to give them an offer they can't refuse, and usually going rate doesn't fit that mark.
Another collector suggested he buy a PAL version of the game / box, another reasonable alternative. Not sure if I would go for that option myself, but on occasion I have taken that route and bought a NES cart, instead of the Famicom version, due to availability.
And many more people suggested that the dude just try to find a copy of the box, and then worry about getting a mint copy down the road, whenever it becomes available. To me, this seems the most reasonable idea. Get a placeholder copy, then sell it and get the nicer one when (IF) it becomes available. With the rares, I have done this so many times, because I would rather have a ratty copy than none at all.
But of course, every suggestion just falls on deaf ears. And thus the community becomes the bad guy for providing good suggestions to help someone obtain an incredibly rare item, and the collector ultimately gets pissed off that he can't find his rare when he wants it, for his price, and decides to sell the rest of his games because of that. The whole thing is just so silly, so stupid if you ask me.