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-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 36.27 euros.
- The coin has been auctioned 18 times, of which it has sold 11 times. This suggests there is consistent interest in the coin.
- In recent auctions, hammer prices have varied, but there are examples of sales reaching up to 140 euros (although this was in an exceptional case).

3. Starting Prices and Estimates:
- The current starting price is 18 euros, and the average starting price in the past has been 25 euros.
- The estimated price for the current auction is 25 euros, indicating that the coin is expected to reach at least that value.

4. Price Trends:
- In recent auctions, hammer prices have ranged from 14 to 45 euros for coins with similar conditions.

Based on these factors, an estimated maximum purchase price could be in the range of 40 to 60 euros, considering that the condition is good and that interest in the coin appears to be consistent. However, since the highest recorded hammer price was 140 euros, it is possible that in an exceptional case, if there is high demand, the price could exceed this range.

Therefore, a reasonable maximum purchase price could be 60 euros.