To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Coin Condition: The coin has a condition rating of 95 (S/C-), indicating that it is in very good shape. This generally increases its value compared to coins with lower conditions.

2. Previous Auction Prices: By looking at the hammer prices from previous auctions for coins with the same condition (95), we can see that they have reached hammer prices of up to 250 euros (in 2018) and 120 euros (in 2020). This suggests that the value of the coin could be quite high.

3. Starting Price and Average Hammer Price: The current starting price is 120 euros, and the average hammer price in previous auctions is 90.88 euros. However, given the high condition, it is reasonable to expect that the hammer price will be above this average.

4. Sales Trends: The coin has been auctioned 30 times, of which it has sold 18 times. This indicates a consistent interest in the coin, which may positively influence its price.

5. Estimated Price: The estimated price for this auction is 150 euros, which is also an important indicator.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 200 to 250 euros, given that there have been precedents of hammer prices in that range and the coin's condition is high. However, considering the starting price of 120 euros, it is likely that the hammer price will not significantly exceed this range unless there is strong competition in the auction.

Therefore, a reasonable maximum purchase price could be 200 euros.