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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in quite good shape. This generally translates to a higher price compared to coins in lower condition.

2. Auction History:
- The coin has been auctioned 17 times, of which it has sold 12 times. This indicates good demand.
- The average hammer price in previous auctions is 68.9 euros, providing a benchmark.
- In past auctions, hammer prices have varied, with a maximum price of 105 euros in 2012.

3. Starting Price and Average Starting Price:
- The current starting price is 70 euros, which is slightly higher than the average starting price of 63.94 euros. This may indicate that the seller has expectations of a higher price due to the condition.

4. Price Trends:
- In recent auctions, prices have shown some variability, but the highest recent hammer price was 70 euros in 2022.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros. This is because, although the average hammer price is 68.9 euros, the good condition of the coin and the history of higher prices suggest that it could reach a higher price in the current auction.

Therefore, a reasonable estimated maximum purchase price could be 90 euros.