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

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- In the past, the coin has been auctioned 6 times, of which it has sold 5 times. This indicates a consistent interest in the coin.
- Previous hammer prices have varied, but the highest was 3200 euros in 2019, when the condition was 85.
- The average hammer price in previous auctions is 1660 euros, which can serve as a reference.

3. Starting Price and Average Starting Price:
- The current starting price is 900 euros, which is below the average starting price of 1090 euros. This may indicate that there is a buying opportunity at a reasonable price.

4. Condition-Based Estimation:
- Given that the current condition is 80, and considering that in the past similar condition coins have sold for prices ranging between 1200 and 1500 euros, we can infer that the hammer price could be in a similar range.

5. Price Trends:
- The trend of hammer prices seems to be increasing, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price for the coin could be between 1200 and 1500 euros, considering that the condition is good and there is a history of hammer prices that supports this estimation. A price of 1400 euros could be a reasonable target, given that it has sold in the past at similar prices.