Based on the data provided, we can observe that the coin in question has had a starting price in previous auctions that has been increasing over time. The coin's condition has remained at a high level, around 85-90 points in previous auctions.

The average auction closing price in previous auctions has been 77.5 euros, with an estimated price in the last auction of 90 euros. Given that the coin's condition remains at a high level and the estimated price in the last auction was 90 euros, we could estimate a maximum purchase price for this coin in the next auction at around 100-110 euros.

Therefore, my recommendation would be to consider a maximum purchase price of around 100-110 euros for this coin in the next auction.