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 very good shape. This generally reduces its value compared to coins in better condition.

2. Previous Prices: By observing previous auction prices, we can see that the coin has had significant price variations depending on its condition. For example:
- In 2013, a coin with a condition of 85 sold for 340 euros.
- In 2022, a coin with a condition of 90 sold for 440 euros.
- In 2021, a coin with a condition of 70 sold for 360 euros.

3. Average Auction Price: The average auction price for previous auctions is 467.14 euros, but this includes coins in better conditions.

4. Starting Price and Average Starting Price: The current starting price is 350 euros, and the average starting price in the past has been 285 euros.

Given that the condition of the coin is quite low (30), it is reasonable to adjust the estimated price downward. Based on previous auction prices and the current condition, a maximum purchase price could be set in a range between 200 and 300 euros.

Estimated maximum purchase price: 250 euros.

This price reflects a balance between the current condition and previous auction prices, considering that the coin is not in optimal condition.