To estimate a maximum purchase price for the coin in question, we can consider several factors:

1. Starting price: 125 euros.
2. Average hammer price: 160 euros. This is an important figure, as it indicates the price at which it has sold in the past.
3. Condition: The coin is in a condition of 90 (EF), which indicates that it is in good shape, potentially increasing its value.
4. Auction history: It has been auctioned once and sold on that occasion, suggesting there is interest in the coin.

Given that the average hammer price is 160 euros and considering that the condition is good, an estimated maximum purchase price could be set slightly above the average hammer price, but not too much, to avoid risking paying more than what the market might be willing to accept.

Therefore, an estimated maximum purchase price could be around 180 euros. This allows for some competition in the auction while also staying within a reasonable range based on historical data.