Oh man! Hahahaha! You're probably right, that should be "Indie" to avoid getting my knickers damp in the future. lol
It varies wildly. If it's a "hero prop" that means it was featured, and usually has close ups on screen. This would be something like the Cricket gun from MIB. Those bring the big money especially if you can match up flaws or damage or any unique thing that proves it's the one used on screen as often there are multiples made but only one makes the final cut.
Background props can be anything and hold far less value, like a coffee mug on a counter in the background.
Also the popularity of the production matters a great deal, props from a blockbuster like Star Wars would bring way more money than something similar from Krull as an example.
Then there's pieces made for rehearsals or stand ins, never seen on film but part of the production. Worth less than screen used by far.
There's also preproduction items like the drawings you mention, storyboards, concept art, etc.
You also have crew items like jackets worn on set or gifts handed out on wrap day, scripts, call sheets, etc. I especially like call sheets because you can see how the movie shooting went, it lists the names of actors and crew and where they will meet and at what times.
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