To estimate a maximum purchase price for the coin that is going to be auctioned, we can analyze the provided data. Here are some key points to consider:

1. Starting price: 250 euros.
2. Average hammer price: 114.8 euros.
3. Auction history: The coin has been auctioned 31 times, of which it has sold 30 times. This indicates good demand.
4. Previous prices: Previous hammer prices varied, but there are examples of auctions reaching up to 300 euros in higher conservation conditions (such as in the auction on 2022-03-30).

Since there is no information about the conservation of the current coin, it is difficult to make an accurate estimate. However, we can consider the starting price and the history of hammer prices.

- The starting price of 250 euros is significantly higher than the average hammer price of 114.8 euros, suggesting that the seller has high expectations for the coin.
- If we consider the highest recorded hammer price (300 euros), this could be a good indicator of a maximum purchase price, especially if the coin has acceptable conservation.

Taking these factors into account, an estimated maximum purchase price could be between 250 and 300 euros, depending on the conservation and demand at the auction. However, since the starting price is 250 euros, a reasonable maximum price could be approximately 275 euros. This allows for some competition in the auction while also remaining below the starting price.