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

1. Condition: The coin has a condition of 70 (MBC-), indicating that it is in an acceptable state, but not of the highest quality. This can influence the price, as coins in better condition tend to fetch higher prices.

2. Previous auction prices:
- In the April 2022 auction, the coin was offered with a starting price of 300 euros and sold for 325 euros, indicating that the market is willing to pay a bit more than the starting price.
- In the September 2024 auction, the starting price was 350 euros, with an estimated price of 450 euros, although it has not yet been sold. This suggests that interest in the coin may be increasing.

3. Average starting and final prices: The average starting price is 308.33 euros and the average final price is 325 euros. This provides additional context on what buyers have been willing to pay.

4. Market trends: Since the coin has only been auctioned twice and has had one sale, the market for this coin is relatively limited, which may make prices more volatile.

Based on these factors, an estimated maximum purchase price could be positioned between the average final price (325 euros) and the estimated price of the next auction (450 euros). However, given that the condition is 70 and considering the price trend, a reasonable maximum price could be approximately 400 euros. This allows for some competition in the auction while also taking into account the condition of the coin.