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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for this coin is 777.74 euros.
- In previous auctions, we have seen hammer prices that vary significantly, but many of them exceed 600 euros, even reaching figures of 1500 euros or more for coins in better condition.
- The last auction of this coin with a similar condition (80) had a hammer price of 900 euros.

3. Starting Price and Estimated Price:
- The starting price is 400 euros, and the estimated price is 900 euros. This suggests that the auctioneers expect the coin to sell for a considerably higher price than the starting price.

4. Sales Trends: The coin has been auctioned 111 times, of which it has sold 103 times, indicating a high sales rate. This may be an indicator of demand and interest in this coin.

Based on these factors, an estimated maximum purchase price could be around 900-1200 euros, considering that the average hammer price is 777.74 euros and that there are examples of previous sales that have exceeded 1000 euros. However, given that the condition is good and there is interest in the coin, a maximum of 1200 euros could be reasonable.