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 (VF-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price for similar coins has been 115.67 euros.
- In previous auctions, coins with similar conditions (around 70) have had hammer prices that varied, but some examples are:
- 55 euros (condition 75)
- 52 euros (condition 80)
- 90 euros (condition 80)
- 130 euros (condition 80)
- The trend shows that coins with conditions from 70 to 80 can reach hammer prices between 50 and 130 euros.

3. Starting Price: The starting price is 18 euros, indicating that the seller expects a lower price initially, but this does not necessarily reflect the actual value of the coin.

4. Previous Prices: In previous auctions, the highest hammer price for coins with similar conditions has been 190 euros (condition 95), but this is an exceptional case.

Based on these factors, an estimated maximum purchase price for the coin with a condition of 70 could be in the range of 80 to 120 euros, considering that the average hammer price is 115.67 euros and that the condition is slightly lower than that of coins that have reached higher prices.

Therefore, a reasonable estimated maximum purchase price could be 100 euros.