To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Condition: The coin has a condition rating of 85 (MS+/EF-), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Current listing price and previous prices: The current listing price is 1300 euros, and the average hammer price in previous auctions is 1121.93 euros. However, the highest recorded hammer price for a coin with a similar condition (85) was 2055 euros in a recent auction.

3. Sales trends: The coin has been auctioned 18 times, of which 14 have been successful sales. This suggests that there is consistent interest in this coin, which may influence its price.

4. Previous hammer prices: Previous hammer prices for coins with similar conditions (80-85) have varied, but the range seems to be between 800 and 1300 euros, with a maximum price of 2055 euros in a recent auction.

Taking these factors into account, an estimated maximum purchase price could be in the range of 1500 to 2000 euros. This is based on the coin's condition, the interest in it, and previous hammer prices. A price of 1500 euros could be a more conservative target, while 2000 euros could be a more optimistic limit, given the interest and condition of the coin.