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

1. Current Condition: The coin has a condition of 80 (MS+), indicating that it is in relatively good shape, but not among the highest qualities.

2. Previous Auction Prices:
- The average hammer price for similar coins has been 2919.29 euros.
- In previous auctions, coins with a similar condition (80) have reached hammer prices of up to 2300 euros.

3. Starting Price and Estimates:
- The current starting price is 1800 euros, which is below the average hammer price.
- The average starting price for similar coins is 1863.16 euros.

4. Recent Trends: In the most recent auctions, hammer prices for coins with a condition of 80 have been in the range of 3000 euros, suggesting an upward trend.

5. Competition Analysis: Given that there is an auction scheduled in the coming days, there is likely to be interest in the coin, which could drive up the hammer price.

Based on these factors, an estimated maximum purchase price could be around 2500-2800 euros. This is based on the analysis of previous hammer prices and the current condition of the coin. However, it is important to note that the final price may vary depending on the competition in the auction and the interest from collectors.