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

1. Condition: The coin to be auctioned has a condition of 85 (ebc-). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Previous auction prices: By analyzing the hammer prices of coins with similar conditions (85 and 95), we can observe that coins with a condition of 95 have reached hammer prices between 3400 and 4000 euros. The last auction of a coin with a condition of 85 had a hammer price of 2600 euros.

3. Average hammer price: The average hammer price for this particular coin is 2980 euros, indicating that, in general, coins of this reference tend to sell within that range.

4. Starting price: The starting price is 1800 euros, which may attract more bidders, but it can also indicate that the seller is looking for a quick sale.

5. Market trends: Since the coin has been auctioned 10 times and all have been sold, this suggests a consistent demand.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 2800 to 3200 euros. This is based on the average hammer price and the condition of the coin. Therefore, a reasonable maximum purchase price could be 3200 euros.