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

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

2. Previous auction prices:
- The average hammer price in previous auctions is 251.58 euros.
- The last auction with a similar condition (85) had a hammer price of 250 euros.

3. Price trends:
- Hammer prices have varied, but generally, coins with similar conditions have reached hammer prices ranging from 220 to 420 euros in the past.
- The highest auction price was 420 euros for a coin with a condition of 95.

4. Current starting price: The starting price is 170 euros, which is below the average hammer price.

Based on this data, an estimated maximum purchase price could be set in a range between 250 and 300 euros, considering that the condition is good and the average hammer price is 251.58 euros.

Therefore, a reasonable estimated maximum purchase price could be approximately 280 euros. This allows for a margin for competition in the auction and aligns with previous hammer prices for similar conditions.