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

1. Current Condition: The coin has a condition of 70 (MS-), which indicates that it is in relatively good shape, although it is not the best possible condition.

2. Auction History:
- The average hammer price in previous auctions is 52.7 euros.
- The coin has been auctioned 11 times, of which it has sold 10 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (like the 70) have varied, but there are examples of sales around 45-70 euros.

3. Starting Price and Average Starting Price:
- The current starting price is 18 euros, which is quite low compared to the average hammer price.
- The average starting price of 31.92 euros also suggests that the current starting price is attractive.

4. Price Trends:
- In recent auctions, hammer prices for coins with similar conditions have been in the range of 40 to 70 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 60 to 70 euros, considering that the condition is good and that the price history suggests that coins in similar conditions have reached those values in the past.

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