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

1. Condition: The coin to be auctioned has a condition of 80 (MS+), which is a fairly good level. In previous auctions, coins with a similar condition have had hammer prices ranging from 1400 to 2300 euros.

2. Previous starting and hammer prices:
- In 2019, the coin with a condition of 80 was auctioned with a starting price of 1200 euros and was hammered at 1400 euros.
- In 2022, the same condition was auctioned with a starting price of 1600 euros and was hammered at 2300 euros.

3. Average hammer price: The average hammer price for previous auctions of this coin is 2025 euros, indicating that, in general, buyers are willing to pay a price higher than the starting price.

4. Current starting price: The current starting price is 1800 euros, which is higher than previous starting prices but also reflects the trend of increasing hammer prices.

Based on these factors, an estimated maximum purchase price could be positioned in a range between the average hammer price (2025 euros) and the highest observed hammer price (2300 euros).

Therefore, a reasonable maximum purchase price could be approximately 2200 euros. This allows for some margin for competition in the auction, considering that the starting price is 1800 euros and that interest in the coin may lead to a hammer price above average.