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 25 (BC), indicating that it is in a fairly deteriorated state. This will negatively affect its value compared to coins in better condition.

2. Previous Auction Prices: By observing the hammer prices of similar coins in the past, we can see that prices have varied considerably. For example:
- In 2020, a coin with a condition rating of 80 was auctioned for 150 euros.
- In 2019, a coin with a condition rating of 70 was auctioned for 75 euros.
- In 2023, a coin with a condition rating of 10 was auctioned for 400 euros, but this is an exceptional case.

3. Average Hammer Price: The average hammer price for similar coins is 194.8 euros, but this includes coins in better condition.

4. Starting Price: The starting price for this coin is 120 euros, which may be a good indicator of its value in the current market.

5. Market Trends: Given that the coin has a history of auctions and has been sold in 59 out of 63 occasions, there is a constant interest in it, although its current condition may limit its appeal.

Taking all these factors into account, an estimated maximum purchase price for this coin, considering its condition and previous hammer prices, could be between 50 and 80 euros. This is based on the price trends for coins in similar conditions and the fact that the current condition is quite low.

Therefore, a reasonable maximum purchase price could be 70 euros.