Background Paragraph: Artworks are sold at affordable prices [6] ranging from £5 to £1500. For many of the works, the price goes up as the edition sells out. The edition runs range from 30 to 10,000 editions. Each work comes with a digital certificate that is “signed, numbered and authenticated by the artist” [7][8] Once an edition is sold out, collectors can resell their works in the online marketplace. 
Story: Bill is an art aficionado. He is searching for some particular pieces to complete his collection. The Stillman edition he wants is still being sold on a normal marketplace, while the Grossman edition of pieces has sold out, and is only available  by private seller.
As more Grossman editions become available for sale will they become more or less expensive? As the Stillman edition sells out, will it become more or less expensive? If Bill wants to start by buying the cheapest editions, which collection should he pay for first? If Bill wants to start his collection by buying the most expensive editions, which should he buy first? Will the Grossman edition of art most likely cost more or less than the Stillman edition? Will the Stillman edition of art most likely cost more or less than the Grossman edition?