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

1. Current Condition: The coin has a condition of 80 (MS+), indicating that it is in relatively good shape. This suggests that its value should be above that of coins with lower conditions.

2. Previous Prices: By looking at previous auction prices, we can see that in past auctions, coins with similar conditions (75 and 80) have reached varying hammer prices. For example:
- In 2016, a coin with a condition of 80 was auctioned with a starting price of 224.39 and an estimated price of 359.03, although the hammer price is not reported.
- In 2022, a coin with a condition of 75 sold for 85.

3. Starting Price and Average Hammer Price: The current starting price is 100 euros, and the average hammer price in previous auctions is 71.67 euros. However, the average starting price of similar coins is 86.68 euros.

4. Sales Trends: The coin has been auctioned 10 times, of which it has sold 5 times. This indicates a moderate interest in the coin, which may influence its price.

5. Price Projection: Given that the condition is good and considering previous hammer prices, a reasonable hammer price for this coin could be in the range of 100 to 150 euros, depending on demand at the auction.

Estimated Maximum Purchase Price: Based on all these factors, an estimated maximum purchase price could be around 120 euros. This takes into account the condition, previous hammer prices, and interest in the coin.