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 relatively good shape, but not of the highest quality (UNC).

2. Historical Prices: By looking at previous auction prices for coins with a similar condition (70), we can see that they have varied. For example:
- In past auctions, coins with a condition of 70 have reached hammer prices of 30 to 60 euros.
- The average hammer price for coins of similar condition seems to be around 30-50 euros.

3. Starting Price and Average Hammer Price: The current starting price is 18 euros, and the average hammer price for this coin in the past has been 104.05 euros. However, since the starting price is significantly lower, this may indicate that the market is adjusting expectations.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have shown a range of 30 to 60 euros, suggesting that interest in coins in this state may be increasing.

Based on these factors, an estimated maximum purchase price for this coin could be between 50 and 70 euros, considering that the condition is an important factor and that interest in VF- quality coins may vary.

Therefore, a reasonable maximum purchase price could be 70 euros.