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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in fairly good shape, although not the best possible condition.

2. Auction History:
- The coin has been auctioned 9 times and has sold on all occasions, suggesting there is demand for this coin.
- The average hammer price in previous auctions is 300 euros, which can serve as a reference.

3. Previous Auction Prices:
- In 2023, a similar coin was auctioned with a hammer price of 530 euros and a condition of 95, indicating that coins in better condition can reach higher prices.
- In 2019, a coin with a condition of 85 sold for 240 euros, suggesting that the price can vary significantly with the condition.

4. Current Starting Price: The starting price is 450 euros, which is higher than the average hammer price of 300 euros, but may be justified by the demand and condition.

5. Maximum Price Estimate: Given that the coin's condition is 80 and considering the price history, a maximum purchase price could be set between the average hammer price and a bit higher, since the starting price is 450 euros.

Taking all these factors into account, an estimated maximum purchase price could be approximately 400 to 450 euros. This would allow for competitive bidding in the auction without exceeding the starting price, while also recognizing the historical value and demand for the coin.