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 quite good shape.

2. Auction History:
- It has been auctioned a total of 13 times, of which it has sold 11 times.
- The average hammer price in previous auctions is 76.73 euros.
- In the most recent auctions, hammer prices have varied, but there are examples of hammer prices exceeding 80 euros, especially for higher conditions.

3. Previous Hammer Prices:
- In 2011, the hammer price was 115 euros in an auction with an unspecified condition.
- In 2022, with a condition of 80, the hammer price was 80 euros.
- In 2023, with conditions of 75 and 80, the hammer prices were 45 and 80 euros, respectively.
- In December 2023, hammer prices reached up to 170 euros for a condition of 95.

4. Starting Price and Estimates:
- The current starting price is 50 euros, and the average starting price in the past has been 47 euros.
- The estimated price for the current auction is 70 euros.

Based on this data, and considering that the condition of the coin is 80 (MBC+), a reasonable maximum purchase price could be in the range of 80 to 100 euros, given that in previous auctions with similar conditions, hammer prices have reached up to 80 euros and more.

Therefore, an estimated maximum purchase price could be 90 euros. This allows for a margin to compete in the auction, considering that the hammer price may vary depending on demand and other factors at the time of the auction.