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

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

2. Auction History:
- The average hammer price for similar coins in the past is 538.13 euros.
- The last auction for this coin had a hammer price of 900 euros (on 2022-03-17) with a condition of 85.
- In other auctions, coins with similar conditions have reached hammer prices that vary, but generally fall between 400 and 700 euros.

3. Starting Price and Estimates:
- The current starting price is 600 euros, which is higher than the average starting price of 416.43 euros.
- The estimated price of 600 euros is also relevant, as it indicates the seller's expectations.

4. Market Trends: Since the coin has been auctioned 42 times and has a sell-through rate of 95% (40 out of 42), this suggests there is consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be around 700-800 euros. This is because, although the starting price is 600 euros, the auction history and current condition suggest that there could be competition in the auction, especially if there are interested collectors.

Therefore, a reasonable maximum purchase price could be 800 euros.