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-), indicating that it is in an acceptable state, but not of the highest quality.

2. Auction History:
- The average hammer price for coins of similar condition (70) in the past has been approximately 50 to 90 euros, with some auctions reaching up to 110 euros.
- In previous auctions, hammer prices for coins with a condition of 70 have varied, but the range seems to be between 40 and 90 euros.

3. Starting Price and Average Hammer Price:
- The current starting price is 20 euros, which is relatively low compared to the average hammer price of 86.06 euros.
- The average starting price of 50.63 euros also suggests that there is potential for an increase in the hammer price.

4. Recent Trends:
- In the most recent auctions, hammer prices have shown a trend of being in the range of 75 to 110 euros for coins of similar condition.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 80 to 110 euros. This is based on the historical hammer prices for coins of similar condition and the potential for an increase in the hammer price in the current auction.