To estimate a maximum purchase price for the coin in question, we can analyze the provided data, including the current condition of the coin, previous auction prices, and behavior in past auctions.

1. 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. Previous auction prices:
- Auction prices for coins with similar condition (80) have varied, but there are examples where they have reached up to 120 euros (as in the auction of October 2020).
- The average auction price for coins in condition 80 in the past has been approximately 38.5 euros.

3. Starting price: The starting price is 25 euros, which is a good starting point, but the final auction price is usually significantly higher.

4. Auction trends: The coin has been auctioned 23 times, with a high sales percentage (21 out of 23). This suggests that there is consistent interest in this coin, which may increase its value at auction.

5. Estimation: Given that the average auction price is 38.5 euros and considering that the condition is good, an estimated maximum purchase price could be between 50 and 70 euros, taking into account that higher prices have been reached in previous occasions.

Therefore, an estimated maximum purchase price for this coin could be between 50 and 70 euros.