To estimate a maximum purchase price for the coin with a grade of 85 (EBC-), we can analyze historical data from previous auctions of coins with a similar grade and their hammer prices.

1. Relevant data from previous auctions:
- In the past, coins with a grade of 85 have had hammer prices ranging from 316 to 401 euros.
- For example:
- 2020-10-20: Hammer price 326 euros (grade 85).
- 2020-11-10: Hammer price 340 euros (grade 85).
- 2023-02-16: Hammer price 375 euros (grade 95, but in a similar range).
- 2023-01-31: Hammer price 420 euros (grade 90).

2. Analysis of starting and hammer prices:
- The current starting price is 400 euros, which is slightly higher than the average hammer price of similar coins in the past (323.88 euros).
- However, the average hammer price for coins with a grade of 85 has been higher on some occasions, reaching up to 401 euros.

3. Estimation of the maximum purchase price:
- Given that the starting price is 400 euros and considering that the hammer price for coins with a grade of 85 has reached up to 401 euros, a reasonable maximum purchase price could be slightly above the starting price, but not much higher to avoid overpaying.
- Therefore, an estimated maximum purchase price could be 450 euros. This allows for a margin to compete in the auction without exceeding the historical value of the coin too much.

In summary, the estimated maximum purchase price for the coin with a grade of 85 would be 450 euros.