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

1. Condition: The coin has a condition rating of 80 (MS+), indicating 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 in previous auctions is €1274.44.
- In past auctions, the coin has reached hammer prices of up to €1900 (in 2020) and €2600 (in 2024, although the latter is a future hammer price).

3. Starting Price: The current starting price is €1800, which is higher than the average starting price of €940, suggesting that the seller has high expectations for this auction.

4. Price Trends: Looking at previous hammer prices, it seems there is potential for the coin to sell for above €1800, especially considering it has reached higher prices in the past.

Given all this, an estimated maximum purchase price could be in the range of €2000 to €2200, taking into account that the highest hammer price in the past was €1900 and that the starting price is €1800. This also considers the possibility that bidders may be willing to compete for the coin, especially if there is interest in its condition and rarity.