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

1. Condition: The coin has a condition of 85 (EBC-), which indicates 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 this coin is 273.54 euros.
- In previous auctions, hammer prices for coins with a similar condition (85) have varied, but there have been hammer prices of up to 280 euros in 2020 and 270 euros in 2020.
- There are also examples of coins with a condition of 95 that have sold for significantly higher prices (650 euros in 2019).

3. Starting Price and Estimates:
- The current starting price is 150 euros, which is quite low compared to the average hammer price.
- The average starting price in the past has been 184.04 euros, suggesting that the current starting price is attractive.

4. Price Trends:
- The general trend seems to be that coins with a condition of 85 have reached hammer prices in the range of 250-280 euros in recent auctions.

Based on these factors, an estimated maximum purchase price for this coin could be around 280-300 euros, considering that the condition is good and the starting price is attractive. This also takes into account the possibility that other bidders may be interested in the coin, which could drive the price up at the auction.