To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the current grade of the coin (75, MS) and previous auction prices for coins with a similar grade.

1. Grade: The coin has a grade of 75 (MS), indicating that it is in quite good condition.

2. Previous auction prices: By looking at the auction prices of coins with a similar grade (75), we find the following relevant data:
- 2021-06-22: Auction price 60 (grade 70)
- 2022-03-16: Auction price 75 (grade 75)
- 2022-04-26: Auction price 70 (grade 85)
- 2022-10-17: Auction price 80 (grade 80)
- 2023-01-18: Auction price 50 (grade 70)

3. Price analysis:
- The highest auction price for a grade of 75 was 75 euros.
- The lowest auction price for a grade of 70 was 50 euros.
- The general trend shows that auction prices for grades between 70 and 85 range from 50 to 80 euros.

4. Maximum price estimation: Since the coin has a grade of 75, and considering that the highest auction price in the past for a similar grade was 75 euros, we can estimate that a reasonable maximum purchase price could be in the range of 70 to 80 euros.

Therefore, an estimated maximum purchase price for this coin could be 75 euros.