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

1. Current Condition: The coin has a condition rating of 80 (MS+), 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 similar coins in the past is 61.41 euros.
- The last auction with a similar condition (80) had a hammer price of 65 euros.
- In previous auctions, hammer prices have varied, but there are examples of coins with a condition of 80 that have sold for 65 euros and 60 euros.

3. Starting Price and Average Starting Price: The current starting price is 40 euros, which is below the average starting price of 43 euros. This suggests that there is potential for the hammer price to be higher.

4. Sales Trends: The coin has been sold in 90% of the auctions it has participated in, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 80 euros, considering that the condition is good and that the hammer price history for similar coins supports this estimate.

Therefore, a reasonable maximum purchase price could be 75 euros.