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

1. Current Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in quite good shape. This suggests that its value should be in the upper range of previous auctions.

2. Previous Auction Prices: By looking at previous auction prices for coins with a similar condition (around 85), we can see that auction prices have varied, but there are examples where prices have reached up to 490 euros (as in the auction on 2019-01-24).

3. Starting Price and Average Hammer Price: The current starting price is 300 euros, and the average hammer price in the past has been 282.81 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Recent Trends: In the most recent auctions, hammer prices have ranged from 320 to 600 euros, indicating growing interest in this coin.

5. Estimation Based on Previous Prices: Given that the condition is good and considering previous hammer prices, an estimated maximum purchase price could be in the range of 400 to 500 euros.

Taking all these factors into account, an estimated maximum purchase price for this coin could be approximately 450 euros. This price reflects both the quality of the condition and the price trends in previous auctions.