I did price the key from Mitsubishi for my 1997 PreFacelift Legnum.
Be sitting down.
They were quoting over $200 for the key blank. (Cant remember the exact price, but it may have been closer to $300. Whichever, far more than it is really worth)
So unless you specifically want an additional Legnum key, with the remote a new car alarm with central locking links would be a cheaper option.