To estimate a maximum purchase price for the coin that is going to be auctioned, we will consider several factors:

1. Condition of the coin: The coin in question has a condition of 80 (MS+), which indicates that it is in relatively good shape, but not among the best qualities.

2. Previous auction prices: By observing the hammer prices of coins with similar conditions (around 80), we can see that they have varied. For example:
- In 2012, a coin with a condition of 80 sold for 28 euros.
- In 2013, another coin with a condition of 80 sold for 23.37 euros.
- In 2014, a coin with a condition of 75 sold for 50 euros.

3. Average hammer price: The average hammer price for this particular coin is 82.61 euros, suggesting that, in general, coins of this reference tend to sell for higher prices.

4. Starting price: The starting price of 50 euros is a good starting point, but given that the average hammer price is significantly higher, it is reasonable to expect that the final hammer price will exceed the starting price.

5. Recent trends: In recent auctions, hammer prices have shown a trend of being higher, as seen in the October 2022 auction, where a similar coin sold for 180 euros.

Taking all these factors into account, an estimated maximum purchase price for the coin in question could be between 80 and 120 euros, considering that the condition is good and that interest in coins of this reference may lead to a higher hammer price.

Therefore, a reasonable estimated maximum purchase price could be 100 euros.