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

1. Current Condition: The coin has a condition of 85 (MBC+/EBC-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current Listing Price and Previous Prices: The current listing price is 300 euros. In previous auctions, coins with a similar condition (85) have had hammer prices that varied, but some have reached up to 700 euros in optimal conditions.

3. Price Trends: The average hammer price for similar coins has been approximately 298.34 euros, suggesting that the hammer price may be close to this value, but given that the condition is good, it could be higher.

4. Sales History: The coin has sold in 94.74% of the auctions it has participated in, indicating high demand.

5. Previous Estimates: In past auctions, coins with a condition of 85 have had hammer prices ranging between 300 and 400 euros, depending on demand and other market factors.

Based on these points, an estimated maximum purchase price for this coin could be between 400 and 450 euros, considering that the condition is good and there is a price history that supports this estimate.