Genuine manufacturer keys and suitable aftermarket keys can have different prices, availability and features. Check the exact part number, key generation, frequency and regional application. A used key may already be locked to another vehicle and may not be suitable for reuse.
If you want to bring your own fob, send its specification before purchasing it. We need to discuss whether it can be registered, which functions are supported and whether coding is available for your model. Keyless entry, push-button start, boot release and remote start should be checked individually where fitted.
A mechanical blade, immobiliser transponder and remote locking can need different work. The car key programming page explains registering a compatible key and the checks required before coding. A repair that preserves the original registered electronics may avoid that extra work.