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

1. Current Condition: The coin has a condition of 75 (MBC), indicating that it is in fairly good shape, but not among the highest qualities.

2. Auction History:
- The average hammer price in previous auctions is 80.59 euros.
- The condition of coins auctioned in the past has varied, but there are examples of coins with similar conditions that have sold for prices ranging from 35 to 140 euros, depending on the condition and demand at that time.

3. Starting Price and Estimated Price:
- The current starting price is 20 euros, and the average starting price in the past has been 50.21 euros. This suggests that the current starting price is relatively low compared to the historical average.

4. Recent Trends: In the most recent auctions, hammer prices have reached up to 110 euros for coins with similar conditions.

Based on these factors, an estimated maximum purchase price could be set in a range between 80 and 120 euros, considering that the coin has a condition of 75 and that interest in the auction may influence the final price.

Therefore, a reasonable maximum purchase price could be 100 euros. This allows for a margin for competition in the auction, given that the average hammer price is 80.59 euros and there are examples of higher sales in the past.