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

1. Current starting price: 1500 euros.
2. Average auction price in the past: 1217.23 euros.
3. Previous auction prices:
- In recent auctions, the hammer prices have ranged from 1800 to 2100 euros for coins in condition 95.
- In the most recent auction, the hammer price was 1800 euros with a condition of 95.

4. Condition: No specific information is provided about the condition of this coin, which may complicate the estimation. However, considering that similar coins have been sold in condition 95 for hammer prices of up to 2100 euros in the past, we can infer that the price could be in a similar range if the condition is good.

5. Price trends: Observing the trends, it seems that prices have been increasing in recent years, especially for coins in good condition.

Given all this, an estimated maximum purchase price could be in the range of 1800 to 2100 euros, assuming the condition of the coin is at least good. If the condition is lower, the price should be adjusted downward.

Therefore, a reasonable maximum purchase price could be 2000 euros.