To estimate a maximum purchase price for the coin that is going to be auctioned, we can analyze the provided data. Here are some key points to consider:

1. Starting price: 50 euros.
2. Auction history: The coin has been auctioned 84 times, of which it has sold 68 times. This indicates good demand.
3. Average hammer price: 41.35 euros, which is lower than the current starting price.
4. Previous prices: There are several hammer prices in the past, with some reaching up to 260 euros in a previous auction, although this may be an exceptional case.
5. Condition: There is no information about the condition of this coin, which may complicate the accurate estimation of its value.

Given that the starting price is 50 euros and considering the average hammer price of 41.35 euros, as well as the fact that there have been previous auctions where higher prices were reached, an estimated maximum purchase price could be in the range of 70 to 90 euros. This is based on the trend of previous prices and the observed demand.

Therefore, an estimated maximum purchase price could be 80 euros.