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

1. Current Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in quite good shape. This is a positive factor that can increase its value.

2. Auction History:
- The average hammer price for similar coins in the past has been 1182 euros.
- In previous auctions, the hammer price has varied, but it has reached up to 2400 euros in a recent auction with a similar condition (85).
- Most coins with a condition of 85 have had hammer prices ranging between 950 and 1400 euros.

3. Starting Price: The current starting price is 1800 euros, which is higher than the average starting price of 983.33 euros. This may indicate that the seller has high expectations, but it could also be an indicator of current demand.

4. Sales Trends: The coin has been sold in 18 of the last 20 auctions, suggesting there is consistent interest in this coin.

5. Comparison with Previous Prices: In previous auctions, coins with a condition of 85 have reached hammer prices of up to 1400 euros, but there is also a recent case where it sold for 2400 euros.

Based on these factors, an estimated maximum purchase price could be between 1800 and 2400 euros, considering that the starting price is 1800 euros and there are precedents for higher sales. However, since the average hammer price has been 1182 euros, a more conservative price could be around 2000 euros, reflecting a balance between the starting price and the sales history.

Therefore, a reasonable estimated maximum purchase price could be 2000 euros.