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 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 previous auction prices for coins with similar conditions (80 and 85), we can see that auction prices have varied. For example, in past auctions, coins with a condition of 80 have reached auction prices of up to 150 euros.

3. Average Auction Price: The average auction price for this coin is 136.65 euros, providing a good reference point.

4. Starting Price: The starting price is 100 euros, indicating that the seller expects a reasonable price for the coin.

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

Taking all these factors into account, an estimated maximum purchase price for this coin could be around 180-200 euros. This is based on the condition, previous auction prices, and market trends.