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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in fairly good shape, but not among the best qualities (FDC).

2. Historical Prices: By looking at previous auction prices for coins of similar condition (around 75-85), we can see that the hammer prices have varied, but generally, they have been in a range of 250 to 420 euros in recent auctions.

3. Starting Price and Average Hammer Price: The current starting price is 450 euros, which is higher than the average hammer price of 317.94 euros. This suggests that the seller has high expectations, but it may also indicate that the market is willing to pay more for this particular coin.

4. Recent Trends: In the most recent auctions, hammer prices for coins of similar condition have been in the range of 380 to 510 euros, suggesting that there is growing interest in coins of good condition.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 450 euros, considering that the starting price is 450 euros and that interest in coins of good condition seems to be increasing. However, since the average hammer price is significantly lower, it would be wise not to exceed 450 euros unless there is strong competition in the auction.

Therefore, a reasonable maximum purchase price could be 450 euros.