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 80 (MBC+). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Starting Price and Average Prices: The current starting price is 90 euros, and the average starting price in previous auctions is 140.36 euros, with an average hammer price of 190.33 euros. This suggests that the coin could sell for a significantly higher price than its starting price.

3. Auction History:
- In the past, the coin has had hammer prices that varied considerably, ranging from 50 euros to 550 euros, depending on the condition.
- The last auction of a coin with a similar condition (85) had a hammer price of 200 euros.

4. Price Trends: Looking at previous auctions, it seems that coins with similar conditions have reached hammer prices ranging between 120 and 300 euros.

Based on these factors, an estimated maximum purchase price for this coin could be in the range of 200 to 250 euros, considering that the condition is good and that the price history suggests it could reach a higher price at auction.

Therefore, a reasonable maximum purchase price could be 250 euros.