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

1. Condition: The coin has a condition rating of 85 (MS+/EF-), 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 in the past is 109.07 euros.
- The last auction with a similar condition (85) had a hammer price of 120 euros.
- In previous auctions, hammer prices have varied, but the highest have been in the range of 300-350 euros for higher conditions.

3. Starting Price and Previous Prices:
- The current starting price is 40 euros, which is relatively low compared to the average hammer price.
- The average starting price in the past has been 70.57 euros, suggesting that the current starting price could be attractive to buyers.

4. Sales Trends: The coin has been sold in 15 out of 17 auctions, indicating good demand.

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 that the hammer price history suggests buyers are willing to pay more for coins in similar conditions.

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