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-), indicating that it is in an acceptable state, but not of the highest quality.

2. Auction History:
- The average hammer price for similar coins has been 66.93 euros.
- In previous auctions, coins with a similar condition (70) have had hammer prices that varied, but some examples are:
- 35 euros in 2018.
- 30 euros in 2022.
- 38 euros in 2020.
- The most recent auction of a coin with a condition of 70 had a hammer price of 18 euros.

3. Starting Price: The current starting price is 18 euros, which is quite low compared to the average hammer price.

4. Price Trends: The average starting price in previous auctions has been 53.41 euros, suggesting there is potential for an increase in the hammer price.

5. Demand and Supply: The coin has been auctioned 70 times in the past, with an 81.4% sell-through rate (57 out of 70). This indicates a consistent interest in this coin.

Based on these factors, an estimated maximum purchase price could be in the range of 40 to 60 euros, considering that the average hammer price is 66.93 euros, but adjusting for the condition and the current starting price.

Therefore, a reasonable maximum purchase price could be 50 euros.