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 (ebc-), which indicates that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price in previous auctions is 522 euros.
- The last auction of this coin with a similar condition (85) had a hammer price of 650 euros in 2016.
- In recent auctions, hammer prices of up to 900 euros have been seen for coins in better condition.

3. Starting Price: The current starting price is 450 euros, which is a good starting point.

4. Price Trends: The overall trend seems to be upward, with hammer prices exceeding 600 euros on several occasions.

Based on these factors, an estimated maximum purchase price could be around 600-700 euros, considering that the condition is good and the price history suggests there is demand for this coin.

Therefore, a reasonable maximum purchase price could be 700 euros.