From Melville House on the process:
The text has been printed in 16-point Baskerville, with type set in hot metal and impressed on thick, mould-made paper. [...]
The case sides for the first volumes were hand marbled... To create the effect, droplets of oil are floated on a solution of caragheen moss and combed into patterns. Since each pattern is different, each book is unique. [...]
The quality of the print and the thickness of the paper meant the presses had to run slowly, with frequent adjustments to ensure evenness of inking and impression. Printing just one of the plays involved eight hours of work a day for six weeks. When the printing was complete the type was melted down, the setting never to be used again. [...]
Each book is half-bound in goatskin from the Sahel region of Nigeria. The leather is tanned in Northamptonshire and then sent to Lachenmaier bindery in Germany. Like many other stages in the production, the binding is executed by hand. [...]
Each volume is individually numbered, titled in 22-carat gold leaf and presented in a buckram-bound solander box. [all emphasis mine]
Each play is a cool $545, and you can get the entire collection for $21,335.
Pocket change, right?