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 70 (MS-), indicating that it is in acceptable condition, but not among the best qualities. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- The average hammer price for coins of similar condition (70) has been approximately 175-190 euros in previous auctions.
- In the auctions where it has sold, the hammer price has ranged between 170 and 195 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 150 euros, which is reasonable given the history of starting and hammer prices.
- The average hammer price of 256.1 euros suggests that there is potential for the coin to sell at a higher price, but this may depend on demand at the auction.

4. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins in superior condition.

5. Auction Expectations: Given that there is an auction scheduled in the coming days, demand may influence the final price. If there is interest, the price could exceed the average.

Based on these factors, an estimated maximum purchase price could be between 200 and 250 euros. This is based on the hammer price history for coins of similar condition and the potential for demand at the auction. However, it is important to note that the final price may vary depending on competition at the auction and other market factors.