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

1. Current Grade: The coin has a grade of 70 (MS-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Prices: Looking at previous auction prices for coins with similar grades:
- In 2020, a coin with a grade of 70 was auctioned for 300 euros.
- Other coins with grades of 80 and 85 have sold between 280 and 380 euros.

3. Starting Price and Average Hammer Price: The current starting price is 350 euros, and the average hammer price in previous auctions is 315.5 euros. This suggests that the market is willing to pay close to this average price.

4. Sales Trends: The coin has been auctioned 11 times, of which it has sold 10 times. This indicates good demand and consistent interest in the coin.

5. Maximum Price Estimate: Given that the grade is 70 and considering previous hammer prices, a maximum purchase price could be around 300-350 euros, as this is the range where coins with similar grades have sold.

Taking all these factors into account, an estimated maximum purchase price for this coin could be 350 euros. This aligns with the starting price and reflects the price trends in previous auctions.