What are some of the more cunning ways people saved money when making films? For example, here are some actors in 80s classic RoboCop wearing catsuits, pretending they have a thermographic camera.

Oh, Tron! I'm probably getting the details wrong, but apparently film stock can be quite inconsistent, and if you don't use it in the right order, you can get sudden flashes of light where the ISO changes for a few frames. Something like that anyway...

The point is, the people making Tron had lots of footage ruined by what looked like occasional flashing lights. So instead of reshooting, they added a "glowing thing passes by" sound effect. (Appropriate of a film set in a computer to turn a bug into a feature!)

For Monty Python and the Holy Grail, they couldn't get actual horses, so they just lampshaded the coconuts instead. What was a constraint ended up becoming one of the film's main running gags. (Admittedly, that kind of fourth wall breaking only really works in comedies.)