I frequent deal with stable isotopes which can happily reach tens of thousands of dollars per gram. In this case ~$70 000 per gram for 41K. In this case I only had about 1/3rd of a gram.
Now it might seem like a lot, but bear in mind this is not really something you can sell. The market for 41K in the entire world is almost nothing. Indeed the only thing that gives it value is it costs so much to make it.
Thankfully, this stuff did good work! We got some of the best measurements on the hydration of potassium in the world!! Indeed they were good enough to highlight some of the previous knowledge about 41K, to the point where I had to bring this sample out of retirement and send it back to the reactor to check the properties of the nucleus.
I wont be adding this to the patreon feed, but many thanks to all those who support this channel! https://www.patreon.com/Thunderf00t