To estimate a maximum purchase price for the coin in question, we will 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 of the highest quality. This may influence the price, as coins in better condition tend to reach higher prices.

2. Auction History:
- In the November 2020 auction, a coin with a condition of 70 was estimated at 30 euros and sold for 40 euros.
- In the June 2021 auction, a coin with a condition of 80 was estimated at 60 euros and sold for 80 euros. This suggests that an improvement in condition can significantly increase the price.

3. Starting Price and Average Prices:
- The current starting price is 18 euros, which is relatively low compared to the average hammer price of 60 euros. This suggests that there is potential for an increase in the final price.

4. Auction Trends: Since the coin has been sold in the past and there have been no failed sale attempts, this indicates that there is interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros, considering that condition is a limiting factor and that the average hammer price in the past has been 60 euros. Therefore, a reasonable maximum purchase price could be 65 euros.