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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in good shape. This is relevant because coins in better condition tend to fetch higher prices at auctions.

2. Auction History:
- It has been auctioned 4 times in the past, and all have sold, indicating a consistent interest in this coin.
- The previous hammer prices have been:
- 260 (condition 70)
- 272 (condition 80)
- 300 (condition 80)
- 261 (condition 70)

3. Current Starting Price: The starting price is 475 euros, which is significantly higher than the previous hammer prices.

4. Average Hammer Price: The average hammer price from previous auctions is 273.25 euros, suggesting that the current starting price is quite high in comparison to the history.

5. Price Trends: Given that the coin's condition is 80, which is the same as in two of the previous auctions, we might expect the hammer price to be in a similar range of 272-300 euros.

Based on this data, an estimated maximum purchase price could be in the range of 300 to 350 euros, considering that the condition is good and there is interest in the coin, but also taking into account that the starting price is quite high and may not be reached in the auction.

Therefore, a reasonable maximum purchase price could be 350 euros.