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 condition 80 has been 50 euros in recent auctions.
- In the past, coins with a condition of 80 have sold for prices that varied, but the range seems to be between 25 and 50 euros, with some exceptional cases reaching up to 70 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 15 euros, which is relatively low compared to the average hammer price of 25.06 euros.
- This suggests that there is potential for the hammer price to be significantly higher.

4. Recent Trends: In the most recent auction, a coin with a condition of 85 sold for 50 euros, indicating that there is growing interest in coins of good condition.

Based on these factors, an estimated maximum purchase price for the coin in condition 80 could be between 40 and 60 euros, considering that the interest in coins of good condition may lead to a higher hammer price. Therefore, a reasonable maximum purchase price could be 50 euros.