I may have misinterpreted the question, but the rambling thoughts are already below..
To me, it's more recognizing a prop base item and having that intrigue my tinkering capacity.
I have no idea how they built them, but that's part of the challenge and the educational research.
Examples: "The most you've spent on something that might make a movie prop" category, in my world of parts-that-are-props:
Loose contextual association: A Galaga from Wargames; Dual purpose. No details necessary other than perhaps a 7-11 Slurpee cup.
doesn't count really but indistinguishable from what was in the film. Midway loaned them a machine, even made placards for the arcade cabinets to cross-promote the film, Is it a prop or just a vintage game? doesn't matter while playing, oh yeah, it's in Wargames. They even played a game sound later in the film for no apparent reason.
And I can always recover my investment as that particular game has standalone value. I could add a switch to a media player that plays 'shall we play a game?' when you put a quarter in? sure. It didn't happen in the movie at that point,, but then again there's that weird phenomenon in the film where Broderick's accessory speech synthesizer module is apparently also installed in all other computers he gets near. The context that accents.
yes, sometimes I do feel I need that prop to finish the detail. Fabricate a speak & spell or ebay one for 20 bucks? Easy.
The trick there is finding the ones with the raised buttons, that's the proper movie one. But if having the later plastic-sheet version motivates me to figure out the E.T. spring-fork-sawblade-record player part, I can always keep looking for a correct one later. Some folks might not even notice the difference. I would.