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+), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that:
- In past auctions, coins with a condition of 80 have reached hammer prices of up to 300 euros (for example, in the auction on 2019-01-24).
- Coins with a condition of 95 have reached hammer prices of up to 460 euros (as in the auction on 2023-01-31).

3. Starting Price and Average Hammer Price: The current starting price is 325 euros, and the average hammer price in the past has been 288.75 euros. This suggests that the starting price is reasonable and could attract bidders.

4. Recent Trends: In the most recent auctions, hammer prices have shown a trend of being higher, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be in the range of 400 to 460 euros, considering that the condition is good and there is potential interest in the coin. Therefore, a reasonable maximum purchase price could be 450 euros.