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

1. Current Condition: The coin has a condition of 80 (MS+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price for similar coins is 496.09 euros.
- In the past, coins with similar conditions (around 80-90) have sold for prices that varied considerably, but some examples are:
- In 2014, a coin with a condition of 90 was hammered at 880.58 euros.
- In 2015, a coin with a condition of 90 sold for 648.28 euros.
- In 2020, a coin with a condition of 85 sold for 420 euros.

3. Starting Price and Average Starting Price: The current starting price is 200 euros, and the average starting price in the past has been 241.29 euros.

4. Sales Trends: Of the 18 times it has been auctioned in the past, 15 have sold, indicating good demand.

Based on this data, an estimated maximum purchase price could be in the range of 400 to 600 euros, considering that a condition of 80 is quite good, but it does not reach the level of higher conditions that have achieved significantly greater prices.

Therefore, a reasonable estimated maximum purchase price could be approximately 500 euros.