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 rating of 80 (MBC+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By looking at previous auction prices for coins with a similar condition (around 80), we can see that they have reached auction prices of up to 120 euros in recent auctions. For example, at the auction on 2021-06-22, a coin with a condition of 85 was sold for 120 euros.

3. Average Auction Price: The average auction price for this coin is 90.14 euros, which can also serve as a reference.

4. Recent Trends: In the most recent auctions, auction prices have shown a trend of increasing, especially for coins in good condition. For instance, at the auction on 2023-01-31, a coin with a condition of 80 was sold for 120 euros.

5. Starting Price: The current starting price is 75 euros, suggesting that the seller expects a final price that could be higher than this.

Considering all these factors, an estimated maximum purchase price for this coin could be between 120 and 150 euros, given that the condition is good and there are precedents for auction prices in that range.

Therefore, a reasonable estimated maximum purchase price could be 130 euros.