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

1. Starting Price: 1800 euros. This is the initial price of the auction.
2. Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape.
3. Auction History:
- In December 2021, the coin was estimated at 3000 euros and sold for 2200 euros.
- In May 2023, it was estimated at 7000 euros, but it did not sell, which may indicate that the starting price was too high or that there were no buyers willing to pay that amount.

4. Average Starting and Final Prices: The average starting price is 3400 euros, and the average final price is 2200 euros. This suggests that, in general, coins of this reference tend to sell for a higher price than the current starting price.

5. Current Demand: The coin will be auctioned in the coming days, which may influence competition and, therefore, the final price.

Taking these factors into account, an estimated maximum purchase price could be positioned between the average final price and the estimated price of the last auction. Given that the average final price is 2200 euros and the estimated price of the last auction was 7000 euros, but it did not sell, it is reasonable to think that a final price around 3000-3500 euros could be a realistic target.

Therefore, an estimated maximum purchase price could be 3500 euros. This allows for a margin for competition in the auction, considering the good condition of the coin and the potential interest from other buyers.