To estimate a maximum purchase price for the coin in question, we can 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 among the best qualities. This can influence the price, as coins in better condition tend to fetch higher prices.

2. Auction History:
- The average hammer price for similar coins is 66.61 euros.
- In the past, coins with similar conditions (80 and 85) have reached hammer prices of 25 to 60 euros.
- The highest recorded auction price was 420 euros for a coin with a condition of 95, indicating that there is a market for high prices, but also that condition is a critical factor.

3. Starting Price and Average Starting Price:
- The current starting price is 15 euros, which is quite low compared to the average starting price of 46.95 euros. This suggests that there may be room for the hammer price to be higher.

4. Sales Trends: The coin has been sold in 18 out of 21 auctions, indicating a consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 40 to 70 euros, considering that condition is a limiting factor and that the average hammer price is 66.61 euros.

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