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

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

2. Previous Auction Prices: By looking at the auction prices of coins with similar conditions, we can see that:
- In previous auctions, coins with conditions of 85 and 95 have reached hammer prices of up to 700 euros (in the case of the condition of 95) and around 460 euros (in the case of the condition of 85).
- The coin in question has a condition of 75, so it is reasonable to assume that its hammer price should be below these values.

3. Average Hammer Price: The average hammer price of similar coins is 418.33 euros. This can serve as a good reference point.

4. Starting Price: The starting price is 450 euros, which indicates that the seller has expectations of a relatively high hammer price.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 400 to 500 euros, considering that the condition of 75 is lower than the conditions of 85 and 95 that have reached higher prices.

Therefore, a reasonable estimated maximum purchase price could be approximately 480 euros. This allows for some competition in the auction, but also reflects the quality of the coin.