To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the current condition of the coin.

1. Current Condition: The coin has a condition of 30 (BC+), which indicates that it is not in the best shape. This may affect its value compared to coins in better condition.

2. Previous Auction Prices:
- In 2018, with a condition of 30, it was auctioned for 35 euros.
- In 2022, also with a condition of 75, it was auctioned for 62 euros.
- In 2019, with a condition of 75, it was auctioned for 55 euros.
- In 2024, with a condition of 30, it was auctioned for 100 euros, which is a notably high price, but it could be an exceptional case.

3. Average Auction Price: The average auction price of similar coins is 60.56 euros, which can serve as a reference.

4. Starting Price: The starting price is 25 euros, indicating that the seller expects a reasonable minimum price.

Given that the condition of the coin is 30, and considering the previous auction prices, an estimated maximum purchase price could be between 35 and 55 euros, taking into account that the highest auction price was 100 euros, but that could be an isolated case.

Therefore, a reasonable estimated maximum purchase price could be 50 euros. This is based on the analysis of previous auction prices and the current condition of the coin.