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

1. Current 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 in the past is 139.3 euros.
- The most recent auction (2023) had a hammer price of 150 euros for a coin with a condition of 75, which is lower than the current condition of 85.
- In 2018, a coin with a condition of 85 was sold for 360 euros, indicating significant potential for high prices for coins in good condition.

3. Starting Price and Average Starting Price: The current starting price is 90 euros, and the average starting price in the past has been 67.27 euros. This suggests that the current starting price is reasonable and could attract bidders.

4. Demand and Supply: Since there have been no unsold coins of this reference in the past, this indicates good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 150 to 200 euros, considering that the condition is better than in recent auctions and that there is a history of high prices for coins in similar conditions.

Therefore, a reasonable maximum purchase price could be 200 euros.