To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 80 (MBC+), 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 starting price for similar coins is 32.52 euros, and the average final price is 36.5 euros.
- In the past, coins with similar conditions (75-90) have been auctioned at prices that varied considerably, but some relevant examples are:
- A coin with a condition of 75 sold for 20 euros and another for 18 euros.
- A coin with a condition of 90 sold for 80 euros.
- A coin with a condition of 80 sold for 41.41 euros.

3. Sales Trends: Out of the 19 times this coin has been auctioned, it has sold 9 times, indicating moderate interest in the coin. However, the fact that it did not sell 10 times may suggest that the starting price is an important factor.

4. Current Starting Price: The starting price is 30 euros, which is slightly below the average starting price of 32.52 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 40 to 50 euros. This is because, given the condition and price history, it is reasonable to expect that a buyer would be willing to pay a little more than the starting price, especially considering that the coin is in relatively good condition.

Therefore, an estimated maximum purchase price could be 45 euros.