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

1. Current Condition: The coin has a condition rating of 80 (MBC+). This is an important factor, as coins in better condition tend to fetch higher prices at auctions.

2. Starting Price and Previous Prices: The current starting price is 100 euros. The average hammer price in previous auctions is 87.76 euros, indicating that, in general, coins of this reference tend to sell for below their starting price.

3. Sales History: Out of the 47 times it has been auctioned, 37 have been sold, indicating a sales rate of 78.7%. This is a good indicator of demand.

4. Previous Hammer Prices: Looking at previous hammer prices, there are several examples of coins with similar conditions that have sold for prices that vary significantly. For example, in 2015, a coin with a condition of 80 sold for 151.65 euros, and in 2022, one with a condition of 85 sold for 210 euros.

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

Based on these factors, an estimated maximum purchase price could be in the range of 120 to 160 euros. This is based on the fact that, although the starting price is 100 euros, the condition of the coin and the price history suggest it could reach a higher price at auction, especially if there is interest among collectors.

Therefore, a reasonable maximum purchase price could be 150 euros.