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 for similar coins in condition 75 has been 65 euros in recent auctions.
- In the past, coins with a condition of 75 have sold for varying prices, but the highest recorded hammer price for a coin of similar condition was 180 euros (although this coin had a condition of 90).

3. Starting Price and Average Starting Price: The current starting price is 25 euros, and the average starting price for similar coins is 57.65 euros. This suggests that the starting price is relatively low compared to the market value.

4. Sales Trends: Out of the 21 times this coin has been auctioned, it has sold 14 times, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the average hammer price for coins of similar condition is 65 euros and that the starting price is low. This also takes into account the possibility that collector interest could drive the price up at auction.

Therefore, a reasonable estimated maximum purchase price would be 80 euros.