I've never really seen much of the original Mission: Impossible. What was it that made the show so dang expensive? Was it the cast salaries, or all the location work they were doing or something?
I can't imagine it was the effects.
One of the interesting elements of Mission: Impossible
was the believability of the gadgets used. There were also speciel effects, but they were obviously much more lowkey than Star Trek's.
Bruce Geller's idea in terms of the gadgets develeped by Barney Collier (Greg Morris) was the device had to actually exist (somewhere) or be plausible in terms of the technology available at the time. Watching the series now some of the gadgets used strike me as maybe too unlikely for the era, but a lot of it should be easy enough today. Yesterday I watched an episode where they used a small hovercraft to maneuver a fair distance along a ventilation shaft. It looked like a small saucer with five or six propellers underneath to provide lift. It was about dinner plate size and really a rather cool looking little thing and conceptually they just might have been able to build one back then. Today we have small radio control helicopters and hovercraft sold as toys that are conceptually similar. But if you have ever played with one of those little RC helicopters you instantly know how susceptible they are to air currents and changes in air density and temperature. They're a pain to keep in level flight and it takes a lot of practice to fly one indoors with any proficciency so I can only imagine the challenge of trying to fly a small gadget of this kind along an air shaft. Also the battery power lasts only a few minutes before it has to be recharged. I seriously doubt they had that kind of lightweight battery power back in the '60s for something that would have needed more power than the toys of today. On the episode they were also flying the little craft essentially blind with only a guiding beacon tied-in to a map for Barney to guide the craft---and he never once bumped into the walls of the air shaft.
But that was often a fascinating element of the show, that it's gadgets were often conceptually sound even if pushed to the limit of what could be possible. And often Bruce Geller wanted the gadgets to be able to function much as described and not just look like they could because of special effects. I can imagine their post production staff scouring piles of issues of popular mechanics for ideas.