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

1. Condition of the coin: The coin has a condition rating of 90 (EBC), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting price and previous prices: The current starting price is 90 euros. In previous auctions, we have seen hammer prices that vary, but there are examples of similar coins that have sold for significantly higher prices, especially those with a similar or better condition.

3. Average hammer price: The average hammer price for similar coins is 101.08 euros, suggesting that the market is willing to pay a bit more than the starting price.

4. Auction trends: The coin has been auctioned 165 times, with an 86.67% sell-through rate (143 out of 165). This indicates a consistent demand for this coin.

5. Recent hammer prices: In the most recent auctions, we have seen hammer prices that exceed the current starting price, suggesting that interest in the coin remains strong.

Based on these factors, an estimated maximum purchase price could be in the range of 120 to 150 euros. This is based on the trend of previous hammer prices and the condition of the coin. However, the final price will depend on the competition in the auction and the interest from other bidders.