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

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

2. Auction History:
- The average hammer price in previous auctions is 1142.31 euros.
- The coin has been auctioned 17 times, of which it has sold 16 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (80-90) have varied, but generally, they have been in the range of 1000 to 1500 euros.

3. Starting Price: The current starting price is 1500 euros, which is higher than the previous average hammer price. This may indicate that the seller has high expectations, but it could also be an indicator that the coin is valued more in the current market.

4. Recent Trends: In the most recent auctions, hammer prices have been in the range of 1200 to 1700 euros for similar conditions.

Based on these factors, an estimated maximum purchase price could be in the range of 1600 to 1800 euros, considering that the condition is good and there is a trend of increasing hammer prices in recent auctions. However, since the starting price is 1500 euros, it is likely that the hammer price will not significantly exceed this value unless there is strong competition among bidders.

Therefore, a reasonable maximum purchase price could be 1700 euros.