To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Starting price: 350 euros.
2. Current condition: 75 (MBC), indicating good preservation.
3. Auction history: The coin has been auctioned 3 times and has sold on all occasions, suggesting consistent demand.
4. Previous prices:
- In the April 2022 auction, the hammer price was 325 euros with a condition of 70.
- In the December 2024 auction, the hammer price was 410 euros, also with a condition of 70.

Given that the current condition is better (75 vs. 70), it is reasonable to expect that the hammer price will be higher than the previous ones.

The average hammer price from previous auctions is 378.33 euros, which can also serve as a reference.

Taking all these factors into account, an estimated maximum purchase price could be around 400-450 euros, considering that the condition is better and that interest in the coin seems to be solid.

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