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

1. Current Condition: The coin has a condition of 70 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- In the auction on November 26, 2021, a coin with a condition of 75 sold for 9 euros.
- In the auction on July 7, 2022, a coin with a condition of 80 sold for 18 euros.
- In the auction on October 18, 2022, a coin with a condition of 70 did not sell, but had an estimated price of 15 euros.

3. Starting Price and Average Price: The current starting price is 6 euros, and the average starting price in the past has been 11 euros, with an average hammer price also of 11 euros.

Given that the condition of the coin is 70, which is similar to the last auction where it did not sell but had an estimated price of 15 euros, and considering that in previous auctions prices of 9 and 18 euros have been reached for higher conditions, we can estimate that the maximum purchase price could be in a range between 10 and 15 euros.

Therefore, a reasonable estimated maximum purchase price for this coin could be 15 euros.