To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Starting Price and Average Hammer Price: The starting price is 1800 euros, and the average hammer price in previous auctions is 1766.46 euros. This suggests that the hammer price is usually close to the starting price.

3. Auction History: The coin has been auctioned 40 times, of which it has sold 36 times. This indicates good demand. Additionally, the average starting price in previous auctions is 1457.35 euros, suggesting that the current starting price is relatively high.

4. Previous Hammer Prices: By observing the hammer prices of coins with similar conditions (80 and 85), we can see that hammer prices have varied, but generally, coins with a condition of 80 have reached hammer prices ranging between 1300 and 2000 euros.

5. Recent Trends: In the most recent auctions, hammer prices have been higher, which could indicate an upward trend in the value of this coin.

Based on these factors, an estimated maximum purchase price could be between 2000 and 2200 euros, considering that the condition is good and there is a trend of increasing hammer prices. However, since the starting price is 1800 euros, it is likely that buyers will be willing to pay a little more, but not much beyond 2200 euros, unless there is significant competition in the auction.