I'm working on a Pathfinder setting that takes place in a modern day version of a fantasy setting. More information is available here.
In working on this setting, I've been using the World of Darkness books. The game's splatbooks offer a wealth of flavor and story ideas for dark settings, and whenever I read one of rulebooks I come away with a lot of ideas that can be incorporated into my Pathfinder setting. I'm reading Midnight Roads (all about travel), and I came across something I want to incorporate.
In World of Darkness, there are Prometheans. To avoid a lengthy talk on backstories, I'm going to compare them to flesh golems that have free will. Numerous differences between the two do exist, but for my purposes they aren't important.
Midnight Roads contains the suggestion that a Promethean might incorporate flesh into their car engine (the examples given being aortic valves pushing oil, pistons made of cartilage, and fleshy fibers filtering fuel), then goes further to suggest that the Promethean may actually be the car.
I like the idea of a flesh golem that actually is a car. Whether or not it has sentience is irrelevant. My wonder is why such a vehicle would be constructed. What is the advantage conferred or point proven by constructing a car out of flesh, which will require a massive amount of magic to achieve? How would such a construct be used to threaten the players (government agents sent to deal with high powered magical threats)? How would a fight between such a construct and characters armed with automatic firearms play out in a challenging manner?
Wouldn't a flesh-golem-horse make more sense? Machinery has too many rotating parts, which simply cannot be alive (or whatever passes for "alive" in the game).
I suppose it may make more sense when it comes to the cost of reanimation, but the rule of cool dictates a car. My initial thought would be to accept the existance of a degree of artificial parts like metal gears so long as more than half the parts are still organic and the car has a pulse.
The other idea that comes to mind is looking like a car on the outside doesn't mean looking like one on the inside. The job of the system of gears that spin the axle can be done with the use of an arm (imagine the way a steam engine's wheels work for what I'm proposing).
How about using the Animate Objects Spell as a baseline? A "Horseless carriage" could be constructed out of just about anything, given a semblance of life via the AO spell, then made permanent.