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+). This is an important factor, as coins in better condition tend to reach higher prices.

2. Previous Prices: By observing previous auction prices for coins with similar conditions (80 and 85), we can see that auction prices have varied. For example:
- In 2020, a coin with a condition of 80 was auctioned for 180 euros.
- In 2021, a coin with a condition of 85 was auctioned for 170 euros.
- In 2023, a coin with a condition of 85 was auctioned for 240 euros.

3. Starting Price and Average Auction Price: The current starting price is 175 euros, and the average auction price for this coin is 166.91 euros. This suggests that the auction price could be in a similar range or slightly above the starting price.

4. Market Trends: Since the coin has been auctioned 37 times in the past and has had a sell-through rate of 97% (36 out of 37), this indicates consistent demand.

5. Price Estimates: Based on previous auction prices and the current condition, a reasonable auction price could be between 180 and 240 euros, considering that the condition of 80 is a limiting factor.

### Final Estimate
Taking all these factors into account, an estimated maximum purchase price for this coin could be 200 euros. This price reflects a balance between the current condition, previous auction prices, and market trends.