To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in good shape, but not the best possible condition.

2. Auction History:
- It has been auctioned 8 times in the past, of which it has sold 6 times.
- The average starting price is 19.4 euros, and the average hammer price is 26.6 euros.
- In previous auctions, hammer prices have varied, but there is a notable price of 50 euros in a 2017 auction, which is the highest recorded.

3. Hammer Prices for Similar Conditions:
- In 2021, a coin with a condition rating of 80 sold for 20 euros.
- In another 2021 auction, a coin with a condition rating of 80 sold for 15 euros.
- In 2024, a coin with a condition rating of 75 sold for 25 euros.

4. Trends:
- The general trend seems to indicate that coins with a condition rating of 80 can reach hammer prices between 15 and 20 euros, although there are exceptions.

Based on this data, an estimated maximum purchase price for the coin in condition 80 could be in the range of 25 to 30 euros, considering that the average hammer price is 26.6 euros and there are precedents of higher hammer prices in similar conditions.

Therefore, a reasonable estimated maximum purchase price could be 30 euros.