To estimate a maximum purchase price for the coin that will be auctioned, we will consider several factors:

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

2. Starting price: The starting price is 3500 euros. This is an important indicator, as it sets the starting point for the auction.

3. Auction history:
- It has been auctioned 34 times in the past, of which it has sold 23 times. This suggests that there is consistent interest in this coin.
- The average hammer price in previous auctions is 30.68 euros, but this seems to be for coins of lower condition, as hammer prices for coins in conditions similar to the current one (100) are significantly higher.
- In previous auctions, hammer prices for coins with a condition of 100 have reached up to 65 euros in the highest recorded case.

4. Recent trends: In the most recent auctions, the hammer price has shown an increase, which could indicate growing interest or value in this coin.

Given that the condition is high and the starting price is considerably higher than previous hammer prices, an estimated maximum purchase price could be a percentage of the starting price, adjusted for the condition and interest in the coin.

Estimation: Considering all these factors, a reasonable maximum purchase price could be in the range of 2000 to 2500 euros, as this represents a significant value in relation to the starting price and the condition of the coin. However, the interest of other bidders in the auction may also influence the final price.