To estimate a maximum purchase price for the coin that will be auctioned, we will consider several factors:

1. Condition of the coin: The coin has a condition rating of 85 (ebc-), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting price: The starting price is 500 euros. This is a good starting point, but not necessarily the final price.

3. Auction history: By looking at previous hammer prices for coins with a similar condition (85), we can see that the hammer prices have varied. For example:
- In previous auctions, coins with a condition of 85 have reached hammer prices of 420 euros (2020-11-10) and 440 euros (2020-02-13).
- There are also examples of coins with a condition of 90 that have sold for 470 euros (2019-09-19) and 500 euros (2022-10-17).

4. Price trends: The average hammer price for similar coins is approximately 399.99 euros, suggesting that the hammer price could be in a similar range.

5. Market expectations: Given that the coin will be auctioned in the near future and has a history of successful sales, it is reasonable to expect that collector interest may drive the price up.

Taking all these factors into account, an estimated maximum purchase price for this coin could be between 500 and 600 euros, considering that the starting price is 500 euros and there is potential for the hammer price to exceed the starting price, especially if there is interest in the auction.

Therefore, a reasonable maximum purchase price could be 600 euros.