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

1. Condition: The coin has a condition rating of 85 (ebc-), indicating that it is in fairly good shape, but not the best possible condition. This may influence the price, as coins in better condition tend to fetch higher prices.

2. Previous auction prices:
- The average hammer price in previous auctions is 344.36 euros.
- The highest hammer prices in the past have been 500 euros (in 2020) and 400 euros (in 2021).
- Most hammer prices have been in the range of 231 to 360 euros.

3. Current starting price: The starting price is 350 euros, which is slightly higher than the average starting price of 252 euros, but is in line with previous hammer prices.

4. Trends: Given that the coin has sold in all previous occasions and considering that the condition is good, it is reasonable to expect that the hammer price will be in a similar range to previous hammer prices.

Based on these factors, an estimated maximum purchase price could be around 400-450 euros. This is based on the fact that the highest hammer price in the past was 500 euros, and since the condition is good, it is likely that bidders will be willing to pay a bit more than the average.

Therefore, an estimated maximum purchase price could be 450 euros.