To estimate a maximum purchase price for the coin in question, we can analyze several factors:

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

2. Auction History:
- The average hammer price for similar coins in the past has been 233.54 euros.
- The condition of the coins auctioned in the past varies, but there are examples of coins with similar conditions (around 70) that have sold for prices ranging from 150 to 480 euros, depending on demand and other factors.

3. Starting Price and Average Starting Price:
- The current starting price is 90 euros, which is relatively low compared to the average starting price of 150 euros for similar coins.
- This suggests that there could be potential for an increase in the hammer price.

4. Recent Trends:
- In the most recent auctions, some coins with similar conditions have reached hammer prices of up to 320 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 200 to 300 euros, considering that the coin has a condition of 70 and that the average hammer price has been 233.54 euros.

Therefore, a reasonable estimated maximum purchase price could be 250 euros. This allows for a margin for competition in the auction, given that the starting price is relatively low.