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

1. 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. Auction history:
- The average hammer price in previous auctions is 20.4 euros.
- The last auction with a known hammer price was 30 euros for a coin with a condition of 100, suggesting that coins in better condition can reach higher prices.
- In previous auctions, hammer prices have varied, but there are examples of similar coins that have reached prices of 25 euros or more.

3. Starting price and estimated prices:
- The current starting price is 9 euros, which is relatively low compared to the average hammer price.
- The estimated price for this auction is 20 euros, which also aligns with previous hammer prices.

Taking these factors into account, an estimated maximum purchase price could be in the range of 25 to 30 euros, given that the condition is high and the price history suggests that coins in similar conditions have reached those values.

Therefore, a reasonable maximum purchase price could be 30 euros.