Could it actually be both? In my experience, cheapness forces bad planning. They don't want to pay for a real project manager, so details get missed. Then you see stuff like last minute budget cuts or weird material swaps that mess up the whole timeline. It creates a cycle where saving money now just costs more later.
Nah I'd say bad planning is the root cause every time. Cheapness is just what happens when the original plan falls apart and they panic. The real problem is nobody thought things through from the start.