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

1. Current Condition: The coin has a condition of 70 (VF-), which indicates that it is in an acceptable state, but not among the best qualities. This can influence the price, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price for similar coins in the past is 63.21 euros.
- In previous auctions, coins with a similar condition (70) have reached hammer prices of 35 euros (2020) and 45 euros (2018).
- There are also examples of coins with higher conditions (80) that have reached hammer prices of 75 euros and 90 euros.

3. Starting Price and Estimates:
- The current starting price is 20 euros, which is relatively low compared to the average hammer price.
- The average starting price of 41.29 euros suggests that there is potential for an increase in the hammer price.

4. Recent Trends: The coin has been auctioned 17 times in the past, with an 82% sell-through rate, indicating consistent interest in this coin.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 60 to 80 euros, considering that the average hammer price is 63.21 euros and that there are examples of similar coins that have reached higher prices.

Therefore, a reasonable maximum purchase price could be 75 euros.