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 80 (MS+), indicating that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Previous Auction Prices: By observing the previous auction prices of coins with a similar condition (80), we can see that they have reached auction prices of up to 420 euros in recent sales.

3. Average Auction Price: The average auction price for this coin is 201.73 euros, providing a solid benchmark.

4. Current Starting Price: The starting price is 150 euros, which is reasonable given the historical auction prices.

5. Recent Trends: In the most recent auctions, the auction prices have shown a trend of increasing, especially for coins in good condition.

Based on these factors, an estimated maximum purchase price could be in the range of 300 to 350 euros. This is based on the coin's potential to reach higher prices depending on its condition and market interest. However, it is important to keep in mind that the final price will depend on the competition in the auction and the demand at that specific moment.