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

1. Current Condition: The coin has a condition of 70 (VF-). This indicates that it is in an acceptable state, but not of high quality. In the past, coins with a similar condition have had auction prices that vary.

2. Auction History:
- In the past, coins with a condition of 70 have been auctioned, and the final prices have been quite variable. For example:
- In 2020, a coin with a condition of 70 was sold for 8 euros.
- In 2018, another coin with the same condition did not sell, but it had a starting price of 12 euros.
- There are also examples of coins with higher conditions (such as 90 or 95) that have sold for significantly higher prices (up to 120 euros).

3. Starting Price and Average Price:
- The current starting price is 12 euros, and the average final price in the past has been 55 euros. This suggests that there is potential for an increase in the final price.

4. Recent Trends:
- In the most recent auctions, final prices have been lower for similar conditions (for example, 20 euros for a condition of 80).

Based on these factors, an estimated maximum purchase price could be between 20 and 30 euros. This is based on the auction price history for coins with similar conditions and the average final price observed.

Therefore, a reasonable maximum purchase price could be 30 euros.