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

1. Current starting price: 1500 euros.
2. Average hammer price in the past: 1543.1 euros.
3. Hammer price history:
- The coin has had hammer prices ranging from 888 euros to 3800 euros, depending on the condition.
- The conditions of the coins auctioned in the past have varied, and the highest hammer prices have been for coins with conditions of 90 or higher.

4. Condition of the current coin: There is no information about the condition of this coin, which makes the estimation more uncertain.

5. Price trends:
- In previous auctions, hammer prices have exceeded the starting price in most cases, especially when the condition is good.
- In recent auctions, hammer prices have been significantly higher than the starting price, especially for coins with conditions of 90 or higher.

Given that the starting price is 1500 euros and considering the average hammer price of 1543.1 euros, as well as the hammer price history showing that coins can reach much higher prices depending on the condition, an estimated maximum purchase price could be:

Estimated maximum purchase price: 2200 euros.

This price is based on the fact that in recent auctions, similar coins have reached hammer prices of up to 2200 euros, especially those with conditions of 90 or higher. However, since there is no information about the condition of this coin, it is advisable to be prepared to adjust the bid according to the evaluation of the coin at the time of the auction.