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 (MS), indicating that it is in quite good shape.

2. Auction History:
- The average hammer price for coins of similar condition (75) has been approximately 38.47 euros.
- In previous auctions, hammer prices for coins with a condition of 75 have varied, but the highest recorded price was 65 euros (in 2016, although the condition is not specified).
- Most coins with a condition of 75 have had hammer prices ranging between 30 and 55 euros.

3. Starting Price: The starting price is 25 euros, which is reasonable and may attract bidders.

4. Price Trends: Given that the coin has been auctioned 23 times in the past and has had a good sales percentage (20 out of 23), this suggests there is consistent interest in this coin.

Based on this data, an estimated maximum purchase price could be in the range of 50 to 65 euros, considering that the condition is good and that interest in the coin appears to be solid. Therefore, a reasonable maximum purchase price could be 60 euros.