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 (VF-), which indicates that it is in relatively good shape, but not of the highest quality. This can influence its value.

2. Auction History:
- The average hammer price of similar coins in the past is 117.43 euros.
- Coins with similar conditions (70) have been auctioned and have reached varied hammer prices, but some have reached significant prices, such as 260 euros in a previous auction with a condition of 95.

3. Starting Price and Estimated Price:
- The current starting price is 20 euros, which is quite low compared to the average hammer price of similar coins.
- The estimated price of 30 euros is also low compared to the historical hammer price data.

4. Sales Trends: The coin has been sold in 14 out of the 17 previous auctions, indicating good demand.

5. Comparison with Previous Prices:
- In previous auctions, coins with similar conditions have reached hammer prices that varied, but some have been significantly higher than the current starting price.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 120 euros, considering that the condition is good and there is a history of hammer prices suggesting it could reach a higher value at auction.

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