Clutch pedal, return springs, and input splines usually don't go bad unless the driver is abusive. So far I haven't replaced any.
Most of the clutch system problems we see at our shop are clutch discs, clutch release bearings, and hydraulics.
If the release bearing goes bad, concentric slave leaks, or clutch is worn out, the vehicle usually gets a clutch kit( clutch disc, pressure plate, pilot bearing, concentric slave cylinder (if equipped), clutch fork pivot ball (if equipped), clutch fork (if worn), the flywheel machined or replaced, and a rear main bearing seal. This all depends on how things are when the transmission is removed.
It just depends on the vehicle and the driver. Not all clutch systems fail the same way.
The cost of clutch replacement or clutch related parts servicing depends on the vehicle. A full blown clutch service is usually around 500-800 US dollars.