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

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

2. Auction History:
- The average hammer price for similar coins in the past is 74.78 euros.
- The coin has been auctioned 10 times, of which it has sold 9 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (70 and 75) have ranged between 35 and 95 euros.

3. Starting Price and Estimates:
- The current starting price is 18 euros, which is relatively low compared to the average hammer price.
- The average starting price for similar coins is 47.8 euros, suggesting that the current starting price could be attractive to buyers.

4. Recent Trends:
- In the most recent auctions, hammer prices have varied, but there are examples of coins with similar conditions that have reached hammer prices of up to 190 euros.

Based on these factors, an estimated maximum purchase price for the coin could be in the range of 70 to 100 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 90 euros.