The current cutoff for prices excludes elements with atomic number greater than 105, including Roentgenium (Latin: Unununium).
Elements above 105, including Roentgenium were excluded as they are highly unstable. Roentgenium, at present, has no known biological role and is only used in research.
Roentgenium was first produced by Peter Armbruster, Gottfried Münzenber and their team working at the Gesellschaft für Schwerionenforschung in Darmstadt, Germany in late 1994.
They bombarded atoms of bismuth-209 with ions of nickel-64 with a device known as a linear accelerator. This produced three atoms of roentgenium-272, an isotope with a half-life of about 1.5 milliseconds (0.0015 seconds), and a free neutron.
Roentgenium's most stable isotope, roentgenium-281, has a half-life of about 26 seconds and decays through spontaneous fission.
Hobart.k12.in.us even describes Roentgenium's cost as unavailable.
Common elements like carbon and oxygen can be made on your own so they don't cost that much. They can be almost given away. But elements like Uranium and Plutonium are incredibly expensive. It all depends on how rare it is and how much you need.