The price difference is significant
As long as a working original key exists, programming an additional key is in many cases significantly easier. If the last key fails, the effort increases noticeably, and the vehicle is out of action in the meantime.
Especially important for used cars
When buying a used car, often only one key is handed over. Check this before purchase and factor a spare key directly into your calculation. For dealers we handle this as a bulk order.
Also relevant for fleets
For company vehicles with changing drivers, a spare key is standard. On request we engrave the keys so assignment within the company stays clear.