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

1. Current Condition: The coin has a condition rating of 75 (VF), indicating that it is in relatively good shape, but not among the highest qualities.

2. Auction History:
- In the past, this coin has been auctioned 4 times and has sold on all occasions.
- Previous hammer prices have been 70, 220, and 45 euros, with conditions of 80 and 85. This suggests that the price can vary significantly depending on the condition.

3. Average Hammer Price: The average hammer price for this coin is 95.25 euros, which can serve as a good indicator of market value.

4. Starting Price: The current starting price is 20 euros, which is quite low compared to the average hammer price.

Given that the coin's condition is 75, which is lower than the conditions of the coins that sold for 220 euros, but higher than the one that sold for 45 euros, we can estimate a maximum purchase price that falls within an intermediate range.

Taking all these factors into account, an estimated maximum purchase price could be around 80-100 euros. This is based on the fact that, although the condition is not the best, the price history and average hammer price suggest that there is significant value in this coin.