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

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

2. Previous Auction Prices:
- In 2020, the coin was auctioned for 70 euros with a condition of 70.
- In 2019, it was auctioned for 140 euros with a condition of 80.
- In 2022, it was auctioned for 220 euros with a condition of 80.

3. Average Auction Price: The average auction price for this coin is 118.33 euros, which is also a good indicator of the expected value.

4. Starting Price: The current starting price is 90 euros, which is reasonable given the price history.

5. Trends: Observing the auction prices, it seems there is an upward trend in auction prices in recent years, especially in 2022.

Given that the condition of the coin is better than that of previous auctions and considering the average auction price, an estimated maximum purchase price could be in the range of 150 to 220 euros, taking into account that the highest auction price in the past was 220 euros.

Therefore, a reasonable estimated maximum purchase price could be 200 euros. This allows for some margin for competition in the auction, given that the starting price is 90 euros.