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

1. Condition of the coin: The coin to be auctioned has a condition of 95 (EBC+), which indicates that it is in very good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous auction prices: By observing the auction prices of coins with similar conditions (95 and close), we can see that they have reached auction prices that vary considerably. For example, in previous auctions, coins with a condition of 95 have reached auction prices of up to 650 euros.

3. Average auction price: The average auction price for this particular coin is 406.91 euros, which can also serve as a reference.

4. Recent trends: In the most recent auctions, the auction prices have shown a range that may be indicative of current demand. For instance, in a recent auction, a coin with a condition of 95 was sold for 10,000 euros, suggesting that there is significant potential for high prices in the future.

5. Starting price: The starting price of 300 euros is a good starting point, but given the history of auction prices, it is likely that the final price will be considerably higher.

Taking all these factors into account, an estimated maximum purchase price for this coin could be in the range of 600 to 800 euros. This is based on the auction price history for coins of similar condition and the trend of increasing prices in recent auctions.