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

1. Condition: The coin has a condition of 70 (MS-), which indicates that it is in relatively good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average starting price from previous auctions is 37.5 euros, and the average hammer price is 61.4 euros.
- In previous auctions, hammer prices have varied, with a maximum of 92 euros and a minimum of 50 euros.

3. Price Trends:
- The last auction with a similar condition (70) had a hammer price of 70 euros.
- The highest recorded auction was 92 euros, suggesting there is potential to reach higher prices depending on demand.

4. Current Starting Price: The starting price is 20 euros, which is relatively low compared to previous hammer prices.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the condition is good and there is a price history that supports this estimate.

Therefore, a reasonable maximum purchase price could be 85 euros.