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

1. Coin Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in relatively good shape. This suggests that its value could be closer to the highest auction prices in the past.

2. Previous Auction Prices: By looking at the auction prices of coins with a similar condition (around 80), we can see that auction prices have varied. For example, in previous auctions, coins with a condition of 80 have reached auction prices of up to 140 euros.

3. Average Auction Price: The average auction price for this coin is 98.02 euros, which can also serve as an indicator of its value.

4. Auction Trends: The coin has been auctioned 209 times, with a sales percentage of 81.7% (171 sold out of 209 auctioned). This indicates a steady demand.

5. Starting Price and Average Starting Price: The current starting price is 40 euros, and the average starting price is 66.21 euros. This suggests that the starting price is relatively low compared to the auction value.

Based on these factors, an estimated maximum purchase price could be in the range of 120 to 150 euros, considering that the condition is good and there are precedents for auction prices in that range for similar coins.

Therefore, a reasonable maximum purchase price could be 150 euros.