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

1. Current Condition: The coin has a condition of 70 (MS-), indicating that it is in an acceptable state, but not of the highest quality.

2. Auction History:
- The average hammer price for coins of similar condition (70) in the past has been approximately 30.67 euros.
- In previous auctions, hammer prices for coins with a condition of 70 have varied, with some examples being:
- 65 euros in December 2018.
- 60 euros in July 2022.
- 40 euros on several occasions.

3. Starting Price: The current starting price is 60 euros, indicating that the seller has reasonable price expectations.

4. Sales Trends: The coin has been auctioned 53 times, of which it has sold 30 times. This suggests there is moderate interest in the coin, but also a significant number of coins that have not sold.

5. Estimated Price: The estimated price of 100 euros in the December 2020 auction for a coin in condition 70 suggests there is potential to reach higher prices, although this depends on demand at the time of the auction.

Based on these factors, an estimated maximum purchase price could be between 60 and 80 euros, considering that the starting price is 60 euros and that, in previous auctions, coins of similar condition have reached hammer prices of up to 65-70 euros. However, if there is strong demand at the auction, it could reach up to 80 euros.