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

1. Condition of the coin: The coin to be auctioned has a condition rating of 95 (S/C-), indicating that it is in very good shape. This is a positive factor that can increase its value.

2. Auction history:
- The average hammer price of similar coins in the past is 39.88 euros.
- Previous auctions show that coins with a similar condition (95) have reached hammer prices of up to 110 euros (in the case of the auction on 2020-03-03).
- Most recent auctions with a condition of 95 have had hammer prices ranging between 20 and 55 euros.

3. Starting price and estimated prices:
- The current starting price is 15 euros, which is relatively low compared to previous hammer prices.
- The estimated price for this auction is not available, but based on the history, it could be in the range of 30 to 50 euros.

4. Sales trends: The coin has been sold in 19 out of the 21 previous auctions, indicating good demand.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros, considering that the condition is high and there is a history of hammer prices that supports this estimate. However, since the starting price is 15 euros, it could be a good opportunity to acquire it at a lower price if the competition in the auction is not high.