To estimate a maximum purchase price for the coin in question, we can analyze the provided data and make some inferences based on previous auctions.

1. Starting and hammer price: The current starting price is 6000 euros, and the average hammer price in previous auctions has been 6910 euros. This suggests that, in general, coins of this reference tend to sell for above their starting price.

2. Auction history: In previous auctions, hammer prices have varied, but it is noted that in auctions where the condition is known (condition value 85), the hammer prices have been 7500 euros and 6300 euros. This indicates that, at least under similar conditions, the hammer price may be in that range.

3. Price estimates: In previous auctions, estimated prices have been higher than the hammer prices. For example, in 2019, the estimated price was 9000 euros, but the hammer price was 7500 euros. This suggests that the estimated price may be a bit optimistic, but still provides a reference point.

4. Condition: Since there is no information about the condition of the current coin, it is difficult to make an accurate estimate. However, considering that coins with a condition of 85 have performed well, we could assume that the coin in question might be in a similar range.

Based on these points, an estimated maximum purchase price could be between 7000 and 8000 euros, considering that the average hammer price has been 6910 euros and that the starting price is 6000 euros. This also takes into account that the market may be willing to pay a little more for a coin that has not been auctioned recently and that could have renewed interest.

Therefore, a reasonable maximum purchase price could be 7500 euros.