To estimate a maximum purchase price for the coin that is going to be auctioned, we can consider several factors:

1. Condition of the coin: The coin in question has a condition rating of 80 (MBC+), which indicates that it is in relatively good shape. This is important because coins in better condition tend to fetch higher prices.

2. Previous auction prices: By looking at the hammer prices of coins with similar conditions, we can see that:
- In the past, coins with a condition rating of 80 have reached hammer prices of up to 280 euros (in 2011).
- The average hammer price for coins of similar condition seems to be around 85.8 euros.

3. Starting price and average starting price: The current starting price is 40 euros, and the average starting price in the past has been 68.32 euros. This suggests that the current starting price is relatively low compared to the historical average.

4. Sales trends: The coin has been auctioned 142 times, of which it has sold 78 times. This indicates that there is considerable interest in this coin, which may influence the hammer price.

Based on these factors, an estimated maximum purchase price could be in the range of 120 to 200 euros, considering that the condition is good and there are precedents for higher hammer prices in the past. However, given the starting price of 40 euros, it is likely that the hammer price will not significantly exceed 200 euros unless there is intense competition among bidders.

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