Given that the coin has a conservation rating of 80 (MBC+), which indicates good quality, and considering that this is the first time it is being auctioned, the starting price is set at 90 euros.

Without historical sales data for this reference, it is difficult to establish a maximum estimated purchase price based on past trends. However, since the starting price is 90 euros and the conservation is good, we could estimate that the final price could be in a range of 90 to 120 euros, depending on the interest from collectors and the competition in the auction.

Therefore, a maximum estimated purchase price could be around 120 euros, assuming there is moderate interest in the coin.