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

1. Current starting price: 1500 euros.
2. Average auction price in the past: 1599.72 euros.
3. Previous auction prices:
- The coin has reached auction prices of up to 2000 euros in a condition of 95.
- In recent auctions, auction prices of 2100 euros and 2400 euros have been seen in conditions of 95 and 85, respectively.

4. Condition of the coin: There is no information about the current condition, which complicates the estimation a bit. However, since similar coins have been sold in the past in a condition of 95 for prices above 2000 euros, we can assume that if the condition is good, the price could be in that range.

5. Price trends: Noting that the average auction price has been 1599.72 euros and that higher prices have been reached in recent auctions, we can consider that interest in this coin may be increasing.

### Estimation of the maximum purchase price:
Given that the highest auction price in the past has been 2400 euros and considering that the starting price is 1500 euros, a reasonable maximum purchase price could be in the range of 2000 to 2400 euros, depending on the condition.

Estimated maximum purchase price: 2200 euros.

This price reflects a balance between market interest, previous auction prices, and uncertainty about the current condition of the coin.