That's a good question.
First of all, they are both icebreakers, so that's the apples to apples comparison, but they're really very different ships. A medium icebreaker is in the range of 6,000 tonnes. A polar icebreaker is a 24,000-tonne ship, so it is a significantly larger ship, with heavier steel, given the higher icebreaking requirements of the ship.
The budget for the polar icebreaker remains under review and will be made public once we get further into the design process. However, it is also a little speculative to try to compare the cost of a used icebreaker to the construction of a new polar icebreaker of a completely different size.