To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in quite good shape. This suggests that its value should be above that of coins with lower conditions.

2. Previous Prices: Looking at previous auction prices for coins with similar conditions:
- In 2019, a coin with a condition of 75 was auctioned for 17 euros.
- In 2018, a coin with a condition of 85 was auctioned for 116 euros.
- In 2021, a coin with a condition of 80 was auctioned for 32 euros.
- In 2022, a coin with a condition of 80 was auctioned for 35 euros.
- In 2023, a coin with a condition of 85 was auctioned for 70 euros.

3. Average Auction Price: The average auction price for this coin is 48 euros, which is also an important indicator.

4. Starting Price and Average Starting Price: The starting price is 20 euros, and the average starting price is 32.73 euros. This suggests that interest in the coin may be moderate, but the auction price could be significantly higher.

5. Auction Trends: Since the coin has been auctioned 12 times and all have been sold, this indicates a consistent interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros, considering that the condition is good and the average auction price is 48 euros. However, given the interest in the coin and its condition, a reasonable maximum purchase price could be 65 euros.