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: 400 euros.
2. Average auction price in the past: 176.44 euros.
3. Previous auction prices:
- The coin has had auctions that varied from 24 euros to 650 euros, depending on the condition.
- The conditions of the auctioned coins in the past have varied, with some reaching conditions of 95, indicating high quality.

4. Condition of the current coin: There is no information about the condition of this coin, which complicates the estimation. However, we can observe that coins with higher conditions have reached significantly higher auction prices.

5. Price trends:
- The general trend shows that coins with higher conditions tend to achieve higher auction prices. For example, a coin with a condition of 95 was auctioned for 650 euros.
- Most auctions have been below 200 euros, suggesting that the average auction price is a good indicator for setting a limit.

Given that the starting price is 400 euros, which is considerably higher than the previous average auction price, and without information about the condition, an estimated maximum purchase price could be set in a more conservative range.

Estimated maximum purchase price: Based on the average auction price and the variability of previous prices, a reasonable maximum purchase price could be between 200 and 250 euros, assuming that the condition is not exceptional. If it is considered that the coin might have a high condition, the price could approach 300 euros, but without clear information, it is better to be conservative.

Therefore, an estimated maximum purchase price could be 250 euros.