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

1. Current starting price: 5500 euros.
2. Coin condition: 95 (S/C-), indicating it is in very good condition.
3. Auction history:
- In 2020, the coin was auctioned with a starting price of 4000 euros and sold for 6000 euros, with a condition of 100.
- In 2024, it was auctioned with a starting price of 3000 euros and sold for 3000 euros, with a condition of 95.

4. Average hammer price: 4500 euros, which is a good indicator of market value.

Given that the current coin has a condition of 95, similar to the 2024 auction, but with a higher starting price, we can infer that the hammer price could be in a similar range or slightly higher than that of the previous auction.

Considering the starting price of 5500 euros and the auction price history, an estimated maximum purchase price could be between 6000 and 6500 euros, given that the condition is good and the interest in the coin seems to be solid.

Therefore, an estimated maximum purchase price could be 6500 euros.