To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Current Condition: The coin has a condition of 100 (MS), indicating that it is in excellent shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Prices: By looking at previous auction prices, we can see that in past auctions, coins with similar conditions have reached hammer prices that vary significantly. For example:
- In 2021, a coin with a condition of 95 was sold for 380 euros.
- In 2020, a coin with a condition of 95 was sold for 280 euros.
- In 2023, a coin with a condition of 90 was sold for 190 euros.

3. Starting Price and Average Hammer Price: The current starting price is 175 euros, and the average hammer price for this coin is 151.54 euros. However, given that the condition is high, it is reasonable to expect that the hammer price will be above this average.

4. Auction Trends: The coin has been auctioned 29 times, of which it has sold 25 times. This indicates good demand and sustained interest in the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 250 to 350 euros, considering that the condition is excellent and that higher prices have been reached in previous auctions for coins in similar conditions.

Therefore, a reasonable maximum purchase price could be 300 euros.