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-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History: The coin has been auctioned 27 times and has had an average hammer price of 266.62 euros. This indicates that, in general, buyers are willing to pay around this price.

3. Previous Auction Prices: By looking at the hammer prices of coins with similar conditions (around 70), we can see that they have reached hammer prices that vary, but have sometimes exceeded 300 euros. For example, in recent auctions, coins with a condition of 70 have sold for hammer prices of 300 euros.

4. Starting Price and Estimates: The current starting price is 275 euros, and the estimated price is 350 euros. This suggests that the seller expects the coin to reach a higher price.

5. Market Trends: Given that there are two auctions scheduled in the coming days, this could generate additional interest and potentially increase the hammer price.

Taking all these factors into account, an estimated maximum purchase price could be around 350-400 euros, considering that the average hammer price has been 266.62 euros and that there is potential for the coin to reach a higher price due to its condition and market demand.

Therefore, a reasonable maximum purchase price could be 400 euros.