Lost your spare? You can take the blade out and take it to a locksmith to get a non-electric one cut.
New full key is £120ish + coding from Renault last time I ordered one (over a year ago).
They have to be ordered in specifically for your hypercar from France.
My understanding is that you can buy a second-hand key, swap out the 'used' key blade for a new one and re-code it to your car's ECU quite simply. Even with only one 'master' key.
I'm currently investigating this route, and will feedback in due course...
...Sod paying £120 for one!!
you can't recode a key thats already been coded. They come from france coded for your immob. All they do at the dealer is program them for your alarm/locking.
strangely, you can have a maximum of 2 keys coded to a car.