To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Condition of the coin: The coin has a condition rating of 85 (ebc-), which indicates that it is in fairly good shape, but not the best possible condition.

2. Previous prices: By looking at the auction prices of coins with similar conditions (85 and 90), we can see that the auction prices have varied. For example, in previous auctions, coins with a condition of 90 have reached auction prices of up to 130 euros, while those with a condition of 85 have had auction prices ranging between 50 and 90 euros.

3. Average auction price: The average auction price for this coin is 69.25 euros, which gives us a good reference point.

4. Recent trends: In the most recent auctions, the auction prices have shown an increase, especially for coins in good condition.

5. Starting price: The starting price is 18 euros, which suggests that there is considerable room for the final price to be higher.

Based on these factors, an estimated maximum purchase price for this coin could be between 80 and 100 euros, considering that the condition is good and there is an upward trend in auction prices in recent sales.

Therefore, a reasonable maximum purchase price could be 100 euros.