To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current condition: The coin has a condition of 75 (MBC), indicating that it is in quite good shape.

2. Auction history:
- In the past, the coin has been auctioned 5 times and has sold on all occasions.
- Previous hammer prices have varied, but the highest was 35 euros (in April 2022) for a coin with a condition of 70.
- The average hammer price for previous auctions is 25.8 euros.

3. Current starting price: The starting price is 20 euros, which is slightly higher than the average starting price of 16 euros.

4. Price trends: Given that the current coin's condition is better (75) than the previous ones (70), it is reasonable to assume that the hammer price could be higher than the previous maximum of 35 euros.

Based on this data, an estimated maximum purchase price could be in the range of 35 to 45 euros, considering that the condition is better and that interest in the coin may have increased. Therefore, a reasonable maximum purchase price could be 40 euros.