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 relatively good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Starting Price and Average Hammer Price: The starting price is 90 euros, and the average hammer price in previous auctions is 136.65 euros. This suggests that, in general, coins of this reference tend to sell for above their starting price.

3. Sales History: The coin has been auctioned 242 times, of which 226 have been sold. This indicates good demand and liquidity in the market for this coin.

4. Previous Prices: Looking at previous hammer prices for coins with similar conditions (around 80), it can be seen that they have reached hammer prices that varied, but some have reached 150 euros or more under similar conditions.

5. Recent Trends: In the most recent auctions, hammer prices have shown an increase, which could indicate an upward trend in the value of this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 150 to 180 euros. This is based on the historical hammer prices and the current condition of the coin. However, it is important to note that the final price may vary depending on the competition in the auction and the demand at the time of sale.