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

1. Current Condition: The coin has a condition rating of 75 (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 hammer price in previous auctions for coins with a similar condition (75) has been approximately 29.1 euros.
- In the most recent auctions, the hammer price for coins with a condition of 75 has been 29 euros (2023-01-18) and 45 euros (2024-07-11), suggesting that there is increasing interest or fluctuations in the market.

3. Starting Price and Average Starting Price: The current starting price is 30 euros, which is slightly higher than the average starting price of 20 euros. This may indicate that the seller has higher expectations due to the coin's condition.

4. Sales Trends: The coin has been sold in 23 out of 25 auctions, indicating good demand. This suggests that buyers are willing to pay competitive prices.

Based on these factors, an estimated maximum purchase price could be in the range of 40 to 50 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 45 euros.