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-). This indicates that it is in an acceptable state, but not of high quality.

2. Historical Prices: By looking at the auction prices of coins with similar conditions (around 70), we can see that the auction prices have varied. For example:
- In previous auctions, coins with a condition of 70 have reached auction prices between 20 and 50 euros.
- Most auction prices for similar conditions are in the range of 20 to 40 euros.

3. Starting Price and Average Auction Price: The current starting price is 15 euros, and the average auction price for this coin in the past has been approximately 47.86 euros. However, given that the current condition is 70, it is likely that the auction price will not reach the highest average.

4. Recent Trends: In the most recent auctions, auction prices for coins with similar conditions have been in the range of 25 to 40 euros.

Based on these factors, an estimated maximum purchase price for this coin could be between 30 and 50 euros, considering that the condition is not the highest and that the starting price is relatively low.

Therefore, a reasonable maximum purchase price could be 40 euros.