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

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price for similar coins is 861.75 euros.
- In previous auctions, hammer prices have varied significantly, ranging from 225 euros to 2400 euros, depending on the condition and other factors.

3. Starting Price and Estimated Price:
- The current starting price is 475 euros, which is slightly higher than the average starting price of 441.39 euros.
- The estimated price for this auction is 800 euros, indicating that the coin is expected to reach a higher price than the starting price.

4. Price Trends:
- In recent auctions, coins with similar conditions have reached hammer prices around 750-950 euros, especially those with condition ratings of 85 or 90.

Based on these factors, an estimated maximum purchase price for this coin could be between 800 and 1000 euros, considering that the condition is slightly lower than coins that have reached higher prices in the past.

Therefore, a reasonable maximum purchase price could be 900 euros. This allows for some margin for competition in the auction, given that the average hammer price is 861.75 euros.