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

1. Coin Condition: The coin has a condition rating of 70 (MS-), which indicates that it is in acceptable condition but not of high quality. This generally affects the price, as coins in better condition tend to fetch higher prices.

2. Auction History: By observing previous hammer prices of coins with similar conditions, we can see that the average hammer price for coins in similar conditions (around 70-80) has varied. For example, in previous auctions, coins with a condition of 70 have reached hammer prices ranging from 140 to 300 euros.

3. Starting Price and Average Hammer Price: The current starting price is 225 euros, and the average hammer price in the past has been 315.21 euros. This suggests that the hammer price could be above the starting price.

4. Recent Trends: In the most recent auctions, we have seen hammer prices exceeding 300 euros for coins in similar conditions.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 300 and 400 euros, considering that the condition and auction history suggest it could reach a higher price, but it is also important to note that the starting price is 225 euros, which could attract more bidders and potentially raise the hammer price.

Therefore, a reasonable maximum purchase price could be 350 euros.