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 of 75 (MBC), indicating that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- It has been auctioned 5 times in the past, of which it has sold 4 times.
- The average hammer price in previous auctions is 61.25 euros.
- Previous hammer prices for coins with a similar condition (75) have varied, but the highest was 65 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 40 euros, and the average starting price in previous auctions is 42.5 euros.

4. Price Trends:
- In previous auctions, hammer prices have fluctuated, but there is a trend for coins with similar conditions to sell above the starting price.

Based on this data, an estimated maximum purchase price could be slightly higher than the previous average hammer price, considering that the condition is good and there is interest in the coin.

Therefore, an estimated maximum purchase price could be around 70 euros. This is based on the hammer price history and the current condition of the coin.