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

1. Current Condition: The coin has a condition rating of 70 (VF-). This is an important factor, as coins in better condition tend to fetch higher prices.

2. Current Starting Price and Previous Prices: The current starting price is 100 euros. In previous auctions, the average hammer price has been 121.93 euros, indicating that similar coins have sold for above their starting price.

3. Sales History: The coin has been auctioned 86 times, of which 78 have been successful sales. This suggests there is consistent interest in this coin.

4. Previous Hammer Prices: Looking at previous hammer prices for coins with similar conditions (70-80), we can see that they have reached hammer prices that vary, but some have gone for 140 euros or more.

5. Recent Trends: In the most recent auctions, hammer prices have shown a range that may indicate an increase in interest or value for the coin.

Based on these factors, an estimated maximum purchase price could be in the range of 140 to 160 euros. This is based on the historical hammer prices for coins of similar condition and the demonstrated interest in previous auctions.

Therefore, a reasonable maximum purchase price could be 150 euros.