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

1. Condition: The coin has a condition rating of 80 (MS+), 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 has been 373.87 euros.
- In previous auctions, hammer prices for coins with a similar condition (80) have varied, but there are examples where hammer prices have reached up to 650 euros (such as in the auction on March 16, 2023).

3. Starting Price: The current starting price is 250 euros, which is a reasonable starting point.

4. Price Trends: Looking at the hammer prices in previous auctions, it seems there is potential for the hammer price to exceed the average price, especially if there is interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 500 to 650 euros, considering that collector interest and the coin's condition may influence the final price.

Therefore, an estimated maximum purchase price could be 650 euros.