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

1. Starting price: 60 euros.
2. Current grade: 75 (MS), which is a fairly good grade.
3. Auction history:
- In the November 2020 auction, the coin sold for 170 euros with a grade of 70.
- In the July 2024 auction, it sold for 75 euros, also with a grade of 70.

4. Average hammer price: 135 euros, indicating that, in general, coins of this reference tend to sell for higher prices than the starting price.

Given that the grade of the coin to be auctioned is better (75) than the previous ones (70), and considering the average hammer price and the price history, we can estimate that the maximum purchase price could be in a range above the average hammer price.

Taking all these factors into account, an estimated maximum purchase price could be around 180-200 euros, given that the grade is better and the price history shows that coins of this reference can reach higher prices in previous auctions.