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.

2. Historical Prices: By looking at previous auction 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 of up to 130 euros.
- The average hammer price for coins of similar condition seems to be around 70-100 euros.

3. Starting Price and Average Hammer Price: The current starting price is 50 euros, and the average hammer price in the past has been 100.37 euros. This suggests that there is potential for an increase in the hammer price.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have shown a range that can reach up to 130 euros, indicating a growing interest in this type of coin.

Based on these factors, an estimated maximum purchase price for this coin could be between 100 and 130 euros, considering that the condition is an important factor and that interest in this type of coin may influence the final price.

Therefore, a reasonable maximum purchase price could be 120 euros.