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 80 (MS+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History: The coin has been auctioned 19 times and has sold on all occasions. This indicates a consistent demand.

3. Previous Hammer Prices: Previous hammer prices for coins with similar conditions (80) have varied, but some relevant prices can be observed:
- In 2022, it was auctioned for 460 and 550 euros.
- In 2023, it was auctioned for 550 euros.
- In 2024, it was auctioned for 420 euros.

4. Average Hammer Price: The average hammer price for this coin is 738.26 euros, suggesting that, in general, buyers are willing to pay more than the starting price.

5. Starting Price and Average Starting Price: The current starting price is 300 euros, and the average starting price is 450 euros. This suggests that the starting price is competitive.

6. Price Estimation: Given that the estimated hammer price for coins in similar conditions has been up to 750 euros, and considering that the condition of this coin is 80, a reasonable maximum purchase price could be in the range of 600 to 800 euros.

### Final Estimation
Taking all these factors into account, an estimated maximum purchase price for this coin could be 750 euros. This is based on the auction price history and the current condition of the coin.