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

1. Starting Price: 40 euros. This is the initial price of the auction.
2. Auction History: The coin has been auctioned 4 times in the past, of which it has sold 2 times. This indicates a moderate interest in the coin.
3. Average Starting and Hammer Price: The average starting price is 83.75 euros and the average hammer price is 90 euros. This suggests that, in general, coins of this reference tend to sell for higher prices than the current starting price.
4. Condition: The coin has a condition rating of 75 (VF), which is a positive factor, as coins in better condition usually fetch higher prices.
5. Previous Prices: In previous auctions, the hammer prices have been 90 euros and 90 euros, with a starting price of 120 euros in one earlier auction.

Given that the average hammer price is 90 euros and considering the condition of the coin, an estimated maximum purchase price could be set in a range between the average hammer price and a bit higher, given that the condition is good.

Therefore, an estimated maximum purchase price could be around 90 to 100 euros. This reflects the interest in the coin and its condition, as well as the price history in previous auctions.