The crucial part is that it is a trash can for a Boeing 707. The first one flew in 1954, and the last one rolled out of the factory in 1994.

So they are either paying for someone to keep it in a warehouse for at least thirty years, paying to keep a trashcan factory around for seventy years, or paying someone to essentially reinvent the wheel and hand-build the damn thing. One-off items are expensive, and one-off aviation items doubly so.