To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition of 85 (MBC+/EBC-), indicating that it is in quite good shape. This suggests that its value should be in the upper range of previous auctions.

2. Auction History:
- The average hammer price in previous auctions is 573.93 euros.
- The last auction with a similar condition (80) had a hammer price of 950 euros.
- In 2022, a coin with a condition of 95 was sold for 900 euros, indicating that coins in good condition can reach high prices.

3. Starting Price: The starting price is 450 euros, which is reasonable and in line with previous starting prices.

4. Price Trends: Observing previous hammer prices, there is a trend for coins in good condition to sell above their starting price, especially if the condition is high.

Based on these points, an estimated maximum purchase price could be in the range of 800 to 950 euros, considering that the coin's condition is good and that there have been previous auctions that reached those prices.

Therefore, a reasonable maximum purchase price could be 900 euros.