The Red key IS important and cannot "be remade for £80" !! How can you remake a unique key with unique codes that are no longer available ??
It contains the codes for all blue keys, so if you were unfortunate enough to lose these, you would need the red key to reprogram the ECU for the replacement keys. No red key in this instance will result in you having to change all the locks on your car, which will cost IRO £1000.
This system, called CODE, was replaced with CODE2 in about 2000, after a spate of incidents involving incompetent numpties, who kept the red key on their main key fob and then lost it. I recall an hilarious Watchdog episode where some **** was bitching about FIAT after losing his red key whilst jogging, even though the Manual clearly states to not use this key (which the Watchdog people clearly pointed out to him) and keep somewhere safe. The moaning idiot complained to FIAT about the £1000 bill, to which he had to pay as no wrong had been done by FIAT. Suffice to say, FIAT changed the system to make it numpty proof.
If the dealer sold you the car without the red key, and told you it didn't need one, you have been misold and are due legal recourse.
If you never lose your blue keys, you will be ok, but it may prove harder to sell without it in the future and you face a big bill if you do lose the blues.