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

1. Coin Condition: The coin has a condition rating of 75 (MBC), which indicates that it is in fairly good shape, but not in mint condition (FDC).

2. Auction History: By looking at the hammer prices of coins with similar conditions (75 and 80), we can see that the hammer prices have varied. For example, in previous auctions, coins with a condition of 80 have reached hammer prices of up to 190 euros, while those rated 75 have had lower, yet still significant, hammer prices.

3. Starting Price and Previous Prices: The current starting price is 18 euros, and the average hammer price in the past has been approximately 98.9 euros. This suggests that there is significant potential for the coin to sell at a higher price.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have shown an increase, which could indicate a growing market.

Based on these factors, an estimated maximum purchase price for this coin could be between 100 and 150 euros, considering that the average hammer price has been 98.9 euros and that there is potential for the price to rise due to demand and the coin's condition.

Therefore, a reasonable maximum purchase price could be 150 euros.