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 of 95 (EF+), indicating that it is in very good shape. This generally translates to a higher price compared to coins in lower condition.

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (95), we can see that they have reached auction prices that vary, but some have exceeded 500 euros. For example, at the auction on 2019-10-17, a coin with a condition of 95 was sold for 495 euros.

3. Starting Price and Average Hammer Price: The current starting price is 400 euros, and the average hammer price for this coin is 340.59 euros. However, given the high condition, it is reasonable to expect that the hammer price will be above the average.

4. Recent Trends: In recent auctions, we have seen that coins with similar conditions have reached hammer prices of up to 1100 euros (as in the auction on 2023-03-16).

5. Estimation Based on Historical Data: Since the coin has been auctioned 81 times and has had a high sales percentage (77 out of 81), this indicates a consistent demand.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 600 to 750 euros. This is based on the condition, previous hammer prices, and the trend of demand in the market.