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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for this coin is 165.8 euros, suggesting that, in general, buyers are willing to pay significantly more than the starting price.
- In previous auctions, hammer prices have varied, but there are examples where the coin has sold for prices close to or above 80 euros, even with similar conditions.

3. Starting Price and Average Starting Price:
- The current starting price is 40 euros, which is relatively low compared to the average hammer price. This may indicate a good opportunity for buyers.

4. Sales Trends: The coin has been sold in 15 out of 19 auctions, indicating good demand. Additionally, the fact that it has not sold in 4 instances may suggest starting prices that were too high or market conditions at those times.

5. Comparison with Previous Prices:
- In previous auctions, the coin has reached hammer prices of up to 135 euros in similar conditions. This suggests that a hammer price in the range of 100-150 euros could be reasonable.

Based on these factors, an estimated maximum purchase price for the coin could be between 100 and 150 euros. This is based on the current condition, the history of hammer prices, and the demand observed in previous auctions.