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

1. Current Condition: The coin has a condition rating of 30 (BC+), indicating that it is not in very good shape. This will negatively affect its value compared to coins in better condition.

2. Auction History:
- The average hammer price for similar coins in the past is 502.8 euros.
- The coin has been auctioned 19 times, of which it has sold 11 times. This suggests that there is moderate interest in the coin.
- Previous hammer prices have varied significantly, with some reaching high prices (for example, 1200 euros in 2013 and 1700 euros in 2020), but there are also lower prices (such as 50 euros in 2014 and 50 euros in 2022).

3. Starting Price: The current starting price is 40 euros, which is relatively low compared to the average hammer price.

4. Price Trends: Hammer prices have fluctuated, but there are examples of coins in similar conditions that have reached hammer prices of up to 400 euros in recent auctions.

Given that the condition of the coin is low and considering the price history, an estimated maximum purchase price could be in the range of 150 to 250 euros. This is based on the fact that, although the coin has a history of high prices, its current state limits its value.

Therefore, a reasonable maximum purchase price could be 200 euros.