To estimate a maximum purchase price for the coin in question, we can 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 40.95 euros.
- The coin has been auctioned 25 times, of which it has sold 21 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (80) have varied, with some selling for 60 euros and others for 40 euros.

3. Starting Price and Estimated Price:
- The starting price is 30 euros, and the average starting price in the past has been 25.29 euros. This suggests that the current starting price is reasonable and could attract buyers.

4. Price Trends:
- In recent auctions, the hammer price has reached up to 60 euros for coins with a condition of 80.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 65 euros.