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

1. Coin Condition: The coin has a condition rating of 70 (MBC-), indicating that it is in an acceptable state, but not among the best qualities.

2. Previous Auction Prices:
- The average hammer price for similar coins has been 99.1 euros.
- In previous auctions, coins with a similar condition (70) have had hammer prices that varied, but some examples are:
- 75 euros (2020-12-14)
- 60 euros (2020-05-26)
- 50 euros (2020-12-14)
- 72 euros (2020-11-10)
- 55 euros (2020-05-26)

3. Starting Price and Average Starting Price:
- The current starting price is 30 euros, and the average starting price for similar coins is 58.55 euros.

4. Price Trends:
- In recent auctions, the hammer price has shown a tendency to be above the starting price, especially for coins in similar conditions.

Based on these factors, an estimated maximum purchase price could be set in a range between 80 and 100 euros, considering that the average hammer price is 99.1 euros and that the coin's condition is acceptable.

Therefore, a reasonable maximum purchase price could be 90 euros. This allows for a margin to compete in the auction without exceeding the historical hammer value for coins in similar conditions.