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

1. Current Condition: The coin has a condition of 70 (MBC-), which indicates that it is in an acceptable state, but not among the best qualities. This can influence the price, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price for this coin in the past is 49.74 euros.
- The last auction with a similar condition (70) had a hammer price of 45 euros.
- In general, hammer prices have varied, with some reaching up to 140 euros in higher conditions (95).

3. Starting Price: The current starting price is 20 euros, which is quite low compared to the average hammer price.

4. Sales Trends: The coin has been auctioned 33 times, of which it has sold 31 times, indicating good demand.

5. Previous Estimates: In previous auctions, the estimated price has varied, but in general, hammer prices have been above the starting price.

Based on these factors, an estimated maximum purchase price could be in the range of 50 to 70 euros, considering that the condition is 70 and the average hammer price is 49.74 euros.

Therefore, a reasonable maximum purchase price could be 65 euros. This is based on the price history and the current condition of the coin.