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), which indicates that it is in fairly good shape, but not among the best qualities (FDC).

2. Auction History:
- The average hammer price for similar coins has been 68.55 euros.
- In the past, coins with similar conditions (around 70-80) have been auctioned and reached varying hammer prices, but some examples are:
- A coin with a condition of 80 was sold for 60 euros.
- Another with a condition of 80 was sold for 90 euros.
- A coin with a condition of 95 was sold for 400 euros, but that is an exceptional case.

3. Starting Price and Estimates:
- The current starting price is 18 euros, which is quite low compared to the average hammer price.
- The average starting price for similar coins is 41.7 euros, suggesting that the starting price might be conservative.

4. Recent Trends:
- In the most recent auctions, hammer prices have ranged from 40 to 90 euros for similar conditions.

Based on these factors, an estimated maximum purchase price for this coin could be between 70 and 90 euros, considering that the condition is good and that the auction history shows that coins in similar conditions have reached those prices.

Therefore, a reasonable maximum purchase price could be 85 euros.