Famicom Disk System dev disk on Mercari

Browsing Mercari Japan, I ran across an FDS dev disk of Lode Runner 2. The seller is asking ¥50,000 which is about $350 USD. Sellers description:

Not for sale Famicom Disk System Sample Super Road Runner. It is the opposite of a normal disk, so if you start it with B and it says "PLEASE SET B", you can play it by switching it to A. Since it is an old product, it will be considered a junk item.

It sounds like the dev flopped A and B when they had written the disk for testing. I suppose it really doesn't matter for in-house testing but it is good to know. Side A more than likely displays an Err 07 meaning its the wrong side of the game to start with. 

$350, to me, seems to be a really hefty price for this piece of gaming history. I was lucky enough to get in on the Sunsoft dev disks a few years ago on eBay for a much lower price. Hopefully this goes to a good home either in Japan or somewhere else in the world.