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 a medium-good quality. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By observing the hammer prices of coins with similar conditions (around 75-80), we can see that the hammer prices have varied. For example:
- In previous auctions, coins with a condition of 75 have reached hammer prices of up to 130 euros.
- Coins with a condition of 80 have reached hammer prices of up to 150 euros.

3. Starting Price and Average Hammer Price: The current starting price is 70 euros, and the average hammer price for this coin is 86.89 euros. This suggests that the market is willing to pay a little more than the starting price.

4. Market Trends: Since the coin has been auctioned 163 times and has had a high sales percentage (142 out of 163), this indicates a steady demand.

Based on these factors, an estimated maximum purchase price could be between 120 and 150 euros, considering that the condition is good and there are precedents for hammer prices in that range.

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