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 (ebc-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History: The coin has been auctioned 73 times and has had an average hammer price of 131.63 euros. This suggests that, in general, buyers are willing to pay around this price.

3. Previous Prices: By looking at previous hammer prices for coins with similar conditions (around 80-85), we can see that they have reached hammer prices that vary, but some have exceeded 200 euros in similar conditions.

4. Starting Price: The starting price of 450 euros is quite high compared to the average hammer price. This may indicate that the seller has high expectations, but it could also deter some buyers.

5. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins in good condition.

Taking all these factors into account, an estimated maximum purchase price could be around 200-250 euros, as this aligns with previous hammer prices for coins of similar condition and considering that the starting price is higher than usual. However, the final price will depend on the competition in the auction and the interest of collectors at that time.