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 quite good shape. This is important because coins in better condition tend to fetch higher prices.

2. Auction History:
- The coin has been auctioned 5 times and has sold in all of them, indicating consistent interest in the coin.
- Previous hammer prices varied, but there is a range from 220 to 320 euros, depending on the condition and market context at each auction.

3. Current Starting Price: The starting price is 425 euros, which is significantly higher than previous hammer prices. This may indicate that the seller expects high interest or that demand has increased.

4. Average Hammer Price: The average hammer price of 262.2 euros suggests that, in general, coins of this reference sell for a price lower than the current starting price.

5. Condition Trends: Observing the conditions of previously auctioned coins, the majority of the higher hammer prices correspond to coins with higher conditions (95 and 85). The coin in question, with a condition of 80, may fall into a lower price range.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 300 to 350 euros. This is based on the history of hammer prices and the current condition of the coin, which, while good, does not reach the levels of coins that have sold for higher prices.