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

1. Current Condition: The coin has a condition of 85 (EF-), which indicates that it is in quite good shape, although it is not the best possible condition.

2. Previous Auction Prices: By looking at the auction prices of coins with a similar condition (85), we find the following relevant data:
- At the auction on September 19, 2019, a coin with a condition of 85 sold for 130 euros.
- At the auction on October 19, 2022, another coin with a condition of 85 sold for 138 euros.
- At the auction on February 14, 2024, it sold for 160 euros.

3. Price Trends: The average auction price for similar coins is 346.66 euros, but this includes coins in better condition. Given that the condition of the coin in question is 85, it is reasonable to adjust our expectations downward.

4. Starting Price: The starting price is 90 euros, which suggests that the seller has moderate expectations.

5. Estimation: Based on the previous auction prices and the current condition, a reasonable maximum purchase price could be in the range of 150 to 180 euros. This is based on the fact that previous auction prices for coins with similar condition have been around 130-160 euros, and given that the market may be willing to pay a bit more in a competitive auction.

Therefore, an estimated maximum purchase price for this coin could be 180 euros.