With their extensive insurance policies, I would guess that AC's out-of-pocket expenses for this incident will be much less than the cost to upgrade their sizable fleet of non-GPS aircraft.
Indeed, AC (and whoever else owns the plane) has probably made a substantial profit on this hull and will have already received the cheque! Airlines insure planes at their full value at the time of purchase, so old birds like this one tend to be worth far less than the policy covering them. And insurers pay out in full within 72 hours of a loss, with policies that cover any and all risks.
BA got paid immediately and in full, for example, when a perfectly serviceable 747 was stranded in Kuwait after the Iraqi invasion. It was the oldest hull in the fleet and earned the company a nice profit. The Iraqis later burned it, long after the cheque had cleared.
The reason for this amazing level of insurance is, of course, the industry's remarkable safety record...