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

1. Condition of the coin: The coin has a condition rating of 80 (MS+), which indicates that it is in quite good shape. This suggests that its value should be above that of coins in worse conditions.

2. Previous auction prices: By looking at the hammer prices of coins with similar conditions (around 80), we can see that the hammer prices have varied. For example:
- In 2019, a coin with a condition of 80 was sold for 80 euros.
- In 2022, another coin with a condition of 80 was sold for 75 euros.
- In 2023, a coin with a condition of 80 was sold for 50 euros.

3. Average hammer price: The average hammer price for this coin is 84.29 euros, which is also a good indicator of the expected value.

4. Starting price: The starting price is 30 euros, which is relatively low compared to previous hammer prices.

5. Market trends: Since the coin has been auctioned 85 times and has had a sell-through rate of 85.88% (73 out of 85), this indicates a consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros, considering that the condition is good and that previous hammer prices have been in that range.

Therefore, a reasonable estimated maximum purchase price could be 90 euros.