Front brakes take the brunt of braking forces - so the front rotor wears faster than the rear. With mechanical disc brakes, the rotor gets pushed in one direction only so wear is also uneven.
For extreme cheapskates, would rotating your rotors front to back make any sense (assuming same size discs)?
Would flipping them make any sense (or even be feasible)?
Flipping is not feasible as rotors are directional in design. You could rotate between wheels ensuring they are in the correct orientation. But I am not sure what you gain, eventually you will need to replace both at once rather than one at a time. Replacing one at a time could make it easier to spread costs out.
While most cable actuated disc brakes move only one moving piston (note there are some dual sided designs out there, e.g., TRP Spyre) the majority of braking (and friction = wear) happens when the moving piston pushes the rotor to come in contact with the stationary side. At this point the friction is pretty even on both side. If you are noticing different wear rates of pads this is likely happening when the brake is not engaged (i.e., rubbing). As such this is more of a set-up issue rather than an issue with not being able to flip the rotor orientation.
If you are worried about rotor life, you should be using organic pads rather than sintered pads, as these use a softer compound. But I am not sure that this would save you money as you will be replacing the organic pads more frequently.
That all said, rotors typically take a very long time to wear especially if the use isn't extreme (e.g., commuting/causual riding versus sessioning a world cup downhill run). If you want to minimized maintenance costs there are other consumables to best focus ones attention on.
For extreme cheapskates, would rotating your rotors front to back make any sense (assuming same size discs)?
Since you mention "extreme cheapskates", I assume you're asking if it would save any money. In the long term, it saves nothing. It might help to think in terms of an analogy. Suppose you have two machines that fill soda bottles (imagine that putting soda into a bottle is putting wear onto a brake rotor). You have a machine that pours two litres per second and a machine that pours one litre per second. Assuming that you move bottles instantaneously between machines, you don't get to fill more (or fewer) bottles per minute by moving part-filled bottles from one machine to another, because your machines still only pour three litres per second between them. So, in any given minute, you fill 90 2-litre bottles, regardless of whether you fill each bottle entirely on one machine or if you part-fill a bottle one one machine and top it off on the other, or transfer them back and forth even more times.
Note, though, that this argument relies on long-term averaging. Since brake rotors last a long time, I guess you're not going to have many replacement rotors over the lifetime of any particular bike. For example (completely making up the numbers, here), suppose that a front rotor lasts five years and a back rotor lasts seven years. If you swap the rotors at the right point, you won't need to replace either rotor in the first six years. Suppose you were going to replace the whole bike anyway after six years: swapping rotors at the right time means you didn't need to buy any replacement rotors; not swapping them means you needed to buy one new rotor.
But Criggie's comment suggests that you're unlikely to need to replace rotors at all, so all of this becomes moot.
