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

1. Coin Condition: The coin has a condition of 70 (MS-), which indicates that it is in an acceptable state, but not of the highest quality.

2. Historical Auction Data:
- The average hammer price for similar coins is 101.08 euros.
- In previous auctions, coins with a similar condition (70) have had hammer prices that vary, but there are examples where they have sold for between 25 and 120 euros.

3. Starting Price and Estimates:
- The current starting price is 15 euros, which is quite low compared to the average hammer price.
- The average starting price for similar coins is 69.06 euros.

4. Sales Trends:
- Out of the 165 times this coin has been auctioned, it has sold 143 times, indicating a good sales rate.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 120 euros, considering that the average hammer price is 101.08 euros and that the coin's condition is acceptable.

Therefore, a reasonable maximum purchase price could be 100 euros.