To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the current grade of the coin (80 - MBC+) and previous auction prices.

1. Grade: The coin has a grade of 80 (MBC+), indicating that it is in quite good condition. In the past, coins with a similar grade have reached auction prices that varied.

2. Previous auction prices:
- In previous auctions, coins with grades of 80 have had hammer prices of 16, 25, and 30 euros.
- The coin with a grade of 95 sold for 260 euros, but that is an exceptional case due to its high grade.
- The coin with a grade of 75 sold for 11 and 40 euros, which also indicates that the price can vary considerably.

3. Average hammer price: The average hammer price for this coin is 54.78 euros, but this includes coins of different grades.

4. Starting price: The current starting price is 15 euros, which is relatively low compared to previous hammer prices.

5. Estimation: Given that the grade is 80 and considering previous hammer prices, an estimated maximum purchase price could be between 30 and 50 euros. However, since the average hammer price is 54.78 euros, we might consider a maximum purchase price closer to this value.

Conclusion: An estimated maximum purchase price for this coin could be approximately 50 euros. This is based on the current grade and previous hammer prices, keeping in mind that the market can vary.