To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Current Grade: The coin has a grade of 70 (MS-), which is a medium level. This suggests that its value should be in line with other coins of similar grade.

2. Auction History:
- The average hammer price for coins with a grade of 70 in the past has been approximately 173.71 euros.
- In previous auctions, hammer prices for coins with a grade of 70 have varied, but they have sold for prices ranging from 120 to 237 euros.

3. Starting Price: The current starting price is 150 euros, which is a reasonable starting point.

4. Price Trends: Observing previous hammer prices, it seems that coins with a grade of 70 tend to sell above the starting price, especially if there is interest in the auction.

5. Estimation: Given that the average hammer price is 173.71 euros and considering that the starting price is 150 euros, a reasonable maximum purchase price could be in the range of 200 to 220 euros, assuming there is competition in the auction.

Therefore, an estimated maximum purchase price for this coin could be 200 euros. This allows for a margin for competition and the interest of other bidders.