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, although it is not the best possible condition.

2. Previous auction prices:
- In the auction on March 1, 2023, the coin sold for 400 euros with a condition of 90.
- In the auction on May 30, 2024, it sold for 300 euros with a condition of 70.
- In the auction on December 11, 2024, it sold for 320 euros also with a condition of 70.

3. Average hammer price: The average hammer price for this coin is 325 euros, which gives us an idea of the market value.

4. Starting price: The current starting price is 250 euros, which can be a good starting point for bidding.

Given that the current condition of the coin is 75, which is better than the conditions of 70 in previous auctions but lower than the condition of 90, we can estimate that the hammer price could be in an intermediate range.

Considering all these factors, an estimated maximum purchase price could be between 350 and 400 euros, since the condition is better than the previous auctions with a condition of 70, but does not reach the level of 90.

Therefore, a reasonable maximum purchase price could be approximately 375 euros.