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

1. Current starting price: 450 euros.
2. Auction history: The coin has been auctioned 12 times and has sold on all occasions, indicating good demand.
3. Average hammer price: 444.42 euros, which is a good indicator of the coin's real market value.
4. Condition: There is no specific information about the condition of this coin, which may make its value somewhat uncertain. However, in previous auctions, coins with conditions of 80-85 have reached hammer prices between 360 and 550 euros.

### Analysis of previous prices:
- The majority of past hammer prices have been in the range of 360 to 550 euros, with an average hammer price of 444.42 euros.
- The highest auction price was 600 euros, indicating that under favorable conditions, the price can exceed 500 euros.

### Maximum price estimation:
Given that the starting price is 450 euros and considering that the average hammer price is 444.42 euros, a reasonable maximum purchase price could be in the range of 500 to 600 euros, especially considering that the coin has a good sales history.

Maximum purchase estimate: 550 euros.

This price reflects a balance between the current starting price and the history of hammer prices, taking into account the lack of information about the specific condition of this coin.