To estimate a maximum purchase price for the coin in question, several factors can be considered, including the coin's condition, previous auction prices, and the average auction price.

1. Coin Condition: The coin has a condition rating of 70 (VF-). This indicates that it is in acceptable condition, but not of high quality (UNC).

2. Previous Auction Prices:
- Several auction prices have been recorded for coins with different levels of condition. For example, coins with a condition rating of 80 have reached auction prices of up to 190 euros, while coins with a condition rating of 90 have reached auction prices of up to 230 euros.
- The trend shows that as the condition improves, the auction price also tends to increase.

3. Average Auction Price: The average auction price for this coin is 98.9 euros, which provides a good reference point.

4. Auction Price Analysis for Similar Conditions:
- For coins with a condition rating of 70, auction prices have varied, but they generally fall within a lower range than coins with higher conditions.
- Based on historical data, an auction price for a coin in VF- condition could be in the range of 40 to 80 euros, depending on demand and other market factors.

5. Final Estimate: Given that the starting price is 15 euros and the average auction price is 98.9 euros, a reasonable maximum purchase price for this coin, considering its condition and previous auction prices, could be between 70 and 90 euros.

Therefore, an estimated maximum purchase price for this coin could be approximately 80 euros.