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+), indicating that it is in relatively good shape, but not the best possible condition.

2. Previous Auction Prices: By looking at previous auction prices, we can see that in past auctions, coins with similar conditions have reached hammer prices that varied significantly. For example:
- In 2018, a coin with a condition of 85 was auctioned for 220 euros.
- In 2022, a coin with a condition of 85 was auctioned for 280 euros.
- In 2022, a coin with a condition of 90 was auctioned for 340 euros.

3. Average Hammer Price: The average hammer price for this coin is 166.07 euros, which gives us a good reference for what buyers are willing to pay.

4. Starting Price and Estimates: The starting price is 70 euros, and the average starting price in previous auctions is 77.5 euros. This suggests that the starting price is reasonable and that there could be interest in the coin.

5. Auction Trends: Since the coin has sold every time it has been auctioned, this indicates a consistent interest in it.

Based on these factors, an estimated maximum purchase price could be in the range of 200 to 250 euros, considering that the condition is good but not excellent, and that there are precedents of higher hammer prices for similar conditions.

Therefore, a reasonable maximum purchase price could be 250 euros.