To estimate a maximum purchase price for the coin in question, we will consider several factors based on the provided data:

1. Current starting price: 250 euros.
2. Auction history: The coin has been auctioned 10 times and has sold on all occasions, indicating good demand.
3. Previous prices:
- The average hammer price in the past has been 180.5 euros.
- In recent auctions, hammer prices have reached up to 320 euros (in 2022) and 290 euros (in 2014).
4. Condition: There is no information on the current condition, but in previous auctions, conditions have varied, with some coins reaching high prices despite not having a specified condition value.

Given that the starting price is 250 euros and considering that in previous auctions hammer prices have exceeded this, an estimated maximum purchase price could be in the range of 300 to 350 euros, depending on the competition in the auction and the interest of collectors.

Therefore, an estimated maximum purchase price could be 350 euros.