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

1. Current Condition: The coin has a condition of 80 (MS+), indicating that it is in relatively good shape, but not the best possible condition.

2. Historical Prices: By looking at previous auction prices for coins with similar conditions, we can see that the average hammer price for conditions between 80 and 85 has been in a range of approximately 200 to 320 euros.

3. Starting Price and Average Hammer Price: The current starting price is 300 euros, and the historical average hammer price is 338.79 euros. This suggests that the hammer price could be in a similar range or slightly above the starting price.

4. Recent Trends: In the most recent auctions, hammer prices for coins with similar conditions have shown an increase, which could indicate a rising trend in interest for these coins.

5. Auction Competition: Given that there are 2 auctions scheduled in the coming days, this could increase competition and, therefore, the hammer price.

Taking all these factors into account, an estimated maximum purchase price could be around 400 euros. This is based on the starting price, the condition of the coin, historical hammer prices, as well as the current trend in the market.