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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price for similar coins has been 39.46 euros.
- In previous auctions, hammer prices have varied, with some reaching up to 90 euros (in the case of a condition of 85) and others in the range of 20 to 55 euros for similar conditions.

3. Recent Trends: In the most recent auctions, hammer prices have been in the range of 30 to 80 euros, depending on the condition.

4. Starting Price and Estimated Price: The starting price is 20 euros, and the estimated price is 40 euros, suggesting that there is potential for an increase in the hammer price.

Given that the condition of the coin is 75 and considering the hammer price history for coins with similar conditions, a reasonable maximum purchase price could be in the range of 60 to 80 euros. This is based on the fact that, although the condition is not the highest, the interest in the coin and the price history suggest that it could reach a higher price at auction.

Therefore, an estimated maximum purchase price could be 70 euros.