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 that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Historical Prices: Looking at previous auction prices for coins with similar conditions:
- In past auctions, coins with a condition of 75 have reached hammer prices of up to 90 euros (as in the auction on 2019-12-10).
- Coins with a condition of 80 have reached hammer prices of up to 120 euros (as in the auction on 2020-02-13).

3. Starting Price and Average Hammer Price: The current starting price is 70 euros, and the average hammer price for this coin is 81.29 euros. This suggests that the market is willing to pay a bit more than the starting price.

4. Auction Trends: Since the coin has been auctioned 46 times and all have been sold, this indicates a steady demand. Additionally, the average starting price has been 49.95 euros, suggesting that interest has been increasing.

Based on these factors, an estimated maximum purchase price could be in the range of 90 to 120 euros, considering that the condition of the coin is good and there are precedents for hammer prices in that range.

Therefore, a reasonable estimated maximum purchase price could be 100 euros. This allows for some margin for competition in the auction, as other bidders may also be interested in the coin.