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 among the best qualities. This generally affects the price, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price in previous auctions is 87.33 euros.
- The last auction with a notable hammer price was in 2022, where the coin reached 650 euros, but this was for a coin in condition 95, which is not directly comparable.
- In 2020, the coin was auctioned with a hammer price of 55 euros, which is more representative of the current condition.

3. Starting Price and Average Starting Price:
- The current starting price is 15 euros, which is quite low compared to the average starting price of 35.27 euros. This suggests that there is potential for the hammer price to be higher.

4. Sales Trends: The coin has been sold in 12 out of 15 auctions, indicating a steady demand.

Based on these factors, an estimated maximum purchase price could be in the range of 70 to 90 euros, considering that the condition is 70 and that the average hammer price in the past has been 87.33 euros.

Therefore, a reasonable maximum purchase price could be 85 euros. This allows for a margin for competition in the auction, given that the starting price is relatively low.