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

1. Current Condition: The coin has a grade of 70 (MS-), indicating that it is in acceptable condition, but not among the best qualities. This affects the price, as coins in better condition tend to reach higher prices.

2. Auction History: By observing previous hammer prices for coins with a similar grade (70), we can see that the hammer price has varied. For example, in previous auctions, coins with a grade of 70 have reached hammer prices ranging from 15 to 25 euros.

3. Average Hammer Price: The average hammer price for this coin is 67.1 euros, but this includes coins of different grades. For a grade of 70, it is reasonable to expect a lower hammer price.

4. Recent Trends: In the most recent auctions, hammer prices for coins with similar grades have been in the range of 15 to 30 euros.

5. Starting Price: The starting price is 15 euros, suggesting that the auctioneer expects moderate interest in the coin.

Taking all these factors into account, an estimated maximum purchase price for this coin, considering its condition and price history, could be in the range of 25 to 35 euros. This would allow for competitive bidding in the auction without exceeding a reasonable limit based on the price history and the current condition of the coin.