To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Coin Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape, but not of the highest quality (FDC).

2. Previous Prices: By looking at the auction prices of coins with similar conditions (around 75), we can see that the auction prices have varied. For example:
- In previous auctions, coins with a condition of 80 have reached hammer prices of up to 63 euros.
- Coins with a condition of 85 have reached hammer prices of up to 210 euros.

3. Average Hammer Price: The average hammer price for this coin is 128.83 euros, suggesting that, in general, coins of this reference tend to sell for relatively high prices.

4. Starting Price: The starting price is 20 euros, which is quite low compared to previous hammer prices.

5. Auction Trends: The coin has been auctioned 266 times, with an 84% sell-through rate, indicating consistent demand.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 100 to 150 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

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