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

1. Starting price: 300 euros.
2. Average starting price: 359.35 euros.
3. Average hammer price: 456.74 euros.
4. Auction history: The coin has been auctioned 27 times, of which it has sold 19 times. This indicates a sales rate of 70.37%, which is quite positive.
5. Condition: There is no specific information about the condition of this coin, but in the history, many of the auctioned coins have a condition of 95 or 100, suggesting that coins in good condition tend to reach higher prices.

Analyzing previous hammer prices, we can observe that:

- In recent auctions, hammer prices have ranged between 340 and 777 euros, depending on the condition and other factors.
- The highest recorded hammer price was 777 euros in 2015, while the lowest in the recent history was 325 euros.

Given that the average hammer price is 456.74 euros and considering that the coin has a starting price of 300 euros, an estimated maximum purchase price could be set in a range that reflects market interest and price trends.

Estimated maximum purchase price:

We could consider a maximum purchase price around 500-600 euros, as this aligns with the estimated prices from previous auctions and the average hammer price. This also takes into account that the coin could be in a condition similar to those that have sold in the past.

Therefore, a reasonable estimated maximum purchase price would be 550 euros.