To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the condition of the auctioned coins.

1. Current starting price: 1500 euros.
2. Average starting price: 1620.69 euros.
3. Average hammer price: 2749.1 euros.
4. Auction price history: Previous hammer prices varied significantly, with some reaching up to 3300 euros in higher condition (such as 95 or 100).

Since there is no information about the condition of the current coin, it is difficult to make an accurate estimate. However, we can observe that:

- Coins with a condition of 80 to 90 have had hammer prices ranging from 1700 to 4000 euros.
- The last auction of a similar coin with a condition of 85 had a hammer price of 2000 euros.

Taking these factors into account, an estimated maximum purchase price could be in the range of 2000 to 3000 euros, depending on demand and competition in the auction.

Therefore, a reasonable maximum purchase price could be 2500 euros. This is based on the average hammer price and the hammer prices of coins with similar conditions in the past.