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

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

2. Historical Prices: By looking at the auction prices of coins with similar conditions, we can see that the highest auction price for a coin with a condition of 30 was 100 euros (at the auction on 2019-12-10). However, there are coins with higher conditions that have sold for significantly higher prices.

3. Average Auction Price: The average auction price for this coin is 477.93 euros, but this includes coins in better condition.

4. Starting Price and Average Starting Price: The current starting price is 225 euros, and the average starting price is 267.21 euros. This suggests that the market is willing to accept a higher starting price than the current one.

5. Sales Trends: The coin has been auctioned 35 times, of which 32 have been sold, indicating good demand.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 100 to 200 euros, given that the condition is not high and the highest auction price for a similar condition was 100 euros. However, if there is interest in the coin and considering the starting price, a reasonable maximum purchase price could be approximately 150 euros.