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

1. Current Condition: The coin has a condition of 75 (MBC), which is a medium level. This suggests that its value will not be as high as that of coins in better condition.

2. Auction History:
- The average hammer price for similar coins in conditions of 75 and 80 has been approximately 270 to 360 euros in previous auctions.
- In particular, the highest recorded hammer price for a coin in condition 80 was 850 euros, but that is an exceptional case.

3. Starting Price and Average Hammer Price:
- The current starting price is 300 euros, which is slightly higher than the average starting price of 261.25 euros.
- The average hammer price of 483.33 euros suggests that there is potential for a higher sale, but this depends on demand at the auction.

4. Price Trends:
- In previous auctions, hammer prices have varied, but the trend seems to be that coins in similar conditions have reached hammer prices in the range of 260 to 650 euros.

Based on these factors, an estimated maximum purchase price for the coin in condition 75 could be in the range of 400 to 500 euros, considering that collector interest may vary and that the hammer price can be influenced by competition at the auction.

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