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), indicating that it is in quite good shape. This generally increases its value compared to coins of lower condition.

2. Auction History:
- In the April 2022 auction, the coin sold for 36 euros with a condition of 25.
- In the March 2024 auction, it sold for 70 euros with a condition of 70.

3. Starting Prices and Average Prices:
- The current starting price is 40 euros, which is higher than the average starting price of 28.33 euros, suggesting an expectation that the coin will sell for a higher price.
- The average hammer price is 53 euros, which also indicates that similar coins have performed well in previous auctions.

4. Supply and Demand: Since there are no upcoming auctions scheduled for this coin, the supply is limited, which could drive up the hammer price.

Taking all these factors into account, an estimated maximum purchase price could be between the average hammer price (53 euros) and the highest observed hammer price (70 euros).

Therefore, a reasonable estimated maximum purchase price could be 65 euros. This reflects a balance between the coin's condition, its sales history, and the expectation of the current auction.