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

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

2. Auction History:
- The average hammer price for similar coins in the past is 44.08 euros.
- There are examples of coins with similar condition (90) that have sold in the past for prices that varied, with some reaching up to 160 euros at auction.

3. Starting Price: The starting price is 35 euros, which is relatively low compared to the average hammer price.

4. Sales Trends: The coin has been auctioned 205 times, with an 84% sell-through rate (173 times sold). This suggests that there is consistent demand for this coin.

5. Previous Prices: Some previous hammer prices for coins in condition 90 have ranged from 40 to 160 euros, indicating a wide range depending on demand at the time of the auction.

Based on these factors, an estimated maximum purchase price could be set in a range between 100 and 150 euros, considering that the condition is good and there is a history of hammer prices that supports this estimate.

Therefore, a reasonable maximum purchase price could be 150 euros.