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

1. Condition: The coin has a condition rating of 100 (MS), indicating that it is in excellent condition. This generally increases its value compared to coins with lower conditions.

2. Auction history:
- The average hammer price for coins with a similar condition (100) has been 75 euros in previous auctions.
- In past auctions, hammer prices have varied, but there are examples of sales that reached up to 110 euros.

3. Starting price and estimates:
- The current starting price is 30 euros, which is reasonable given the history of starting and hammer prices.
- The average hammer price is 39.88 euros, suggesting that the coin could sell for a price higher than the starting price.

4. Recent trends: In the most recent auctions, hammer prices have shown a range that can be higher, especially for coins in optimal condition.

Based on these factors, an estimated maximum purchase price for this coin could be between 80 and 100 euros, considering that the condition is excellent and there are precedents for high hammer prices in the past. However, given the starting price of 30 euros, it is likely that the final hammer price will be closer to the lower end of this range unless there is significant competition among bidders.

Therefore, a reasonable maximum purchase price could be 90 euros.