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

1. Condition: The coin to be auctioned has a condition of 70 (MS-). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Previous Prices: By observing the hammer prices of coins with similar conditions, we can see that:
- In 2011, a coin with a condition of 75 sold for 336 euros.
- In 2012, the same condition (75) reached a price of 750 euros.
- In 2020, a coin with a condition of 70 sold for 100 euros.
- In 2022, a coin with a condition of 80 sold for 300 euros.

3. Starting Price and Average Prices: The starting price of the coin is 650 euros, and the average hammer price in previous auctions is 417.11 euros. This suggests that the starting price is relatively high compared to the average hammer price.

4. Sales Trends: The coin has been auctioned 12 times in the past, of which it has sold 8 times. This indicates that there is interest in the coin, but also that there is a 33% chance it has not sold, which may influence the perception of its value.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 400 to 600 euros, considering that the starting price is 650 euros and the average hammer price is 417.11 euros. However, given that the condition is 70, which is lower than other coins that have sold for higher prices, a reasonable maximum purchase price could be approximately 550 euros. This allows for some competition in the auction, but also reflects the reality of the market based on historical data.