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

1. Coin Condition: The coin has a condition rating of 100 (S/C), indicating that it is in excellent condition. This generally translates to a higher price compared to coins with lower condition ratings.

2. Auction History:
- In the past, this coin has had hammer prices that vary significantly. The highest recorded price was 110 euros at an auction in December 2020, with a starting price of 90 euros.
- The average hammer price for coins of similar condition (100) is also an important indicator. Although there is not much specific data for this condition, the overall average hammer price is 34.38 euros.

3. Starting Price and Estimated Price: The current starting price is 30 euros, and the average starting price in the past has been 19.71 euros. This suggests that the current starting price is relatively high, but not unusual for a coin in excellent condition.

4. Sales Trends: The coin has been sold in 35 out of 38 auctions, indicating good demand and sustained interest in this reference.

Based on these factors, an estimated maximum purchase price could be in the range of 100 to 120 euros, considering that the condition is excellent and there have been precedents for hammer prices in that range. However, since the starting price is 30 euros, it is likely that the hammer price will not significantly exceed the previous estimated price. Therefore, a reasonable maximum purchase price could be approximately 100 euros.