The last offer of 15bil was current outbid this morning.
The last sellers with prices and dates according to the forum are as follows, to give you an idea of the price of this item, one of the rarest items in the games, even more so than AT ships:
August 2021 - 25bil - WTS Mobile Refinery Operation skillbook - #5)
May 2021 - 35bil- WTS Collectors Mobile Refinery Operation skill + original Large rigged ships
April 2021 - 35bil with an offer of 30bil - WTS rare skillbooks