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 of 85 (ebc-), which indicates that it is in fairly good shape, but not the best possible condition. This may influence the price, as coins in better condition tend to reach higher prices.

2. Historical Prices:
- In previous auctions, we have seen hammer prices that vary considerably. For example, in 2011, a coin with a condition of 90 sold for 1807.06 euros, and in 2013, another with the same condition sold for 4823.41 euros.
- In more recent auctions, coins with a condition of 80 sold for 900 euros and 700 euros.

3. Average Hammer Price: The average hammer price for this coin is 1866.09 euros, which gives us a good reference for the value that buyers are willing to pay.

4. Starting Price: The current starting price is 370 euros, which is significantly lower than the average hammer price.

5. Sales Trends: The coin has sold in 5 of the last 6 auctions, indicating a consistent interest in this reference.

Based on these factors, and considering that the condition of the coin is slightly lower than those that have reached higher prices, an estimated maximum purchase price could be set in a range between the average hammer price and a bit less, given its condition.

Estimated Maximum Purchase Price: It could be reasonable to estimate a maximum purchase price of around 1500 to 1700 euros. This reflects an interest in the coin, but also takes into account its current condition.