To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the condition of the coin.

1. Condition of the coin: The coin to be auctioned has a condition of 95 (EBC+), indicating that it is in very good condition. This is relevant because coins in better condition tend to fetch higher prices at auctions.

2. Previous auction prices: By looking at the auction prices of coins with a similar condition (95) in the past, we can see that prices have varied. For example:
- In December 2020, a coin with a condition of 95 was auctioned for 350 euros.
- In March 2021, another coin with a condition of 95 was auctioned for 326 euros.
- In June 2022, a coin with a condition of 95 was auctioned for 390 euros.

3. Starting price and average auction price: The starting price of the coin is 450 euros, and the average auction price for similar coins is 275.7 euros. However, since the condition of this coin is high, it is likely that the auction price will be above average.

4. Recent trends: In the most recent auctions, the auction prices for coins with a condition of 95 have ranged from 350 to 460 euros, suggesting that interest in coins in good condition has increased.

Based on these factors, an estimated maximum purchase price for this coin could be between 450 and 500 euros, considering that the starting price is 450 euros and that the condition is high. This also takes into account the possibility that bidders may be willing to pay a little more for a coin in such good condition.

Therefore, an estimated maximum purchase price could be 500 euros.