To estimate a maximum purchase price for the coin in question, let's consider several factors:

1. Current Condition: The coin has a condition of 70 (VF-), which is lower than the conditions of previously auctioned coins (75). This could influence the price, as a lower condition generally translates to a lower price.

2. Previous Prices:
- In the December 2020 auction, the coin sold for 200 euros, which was both the starting price and the final price.
- In the May 2023 auction, the coin sold for 310 euros, although the starting price was 200 euros. This indicates an increase in interest or value of the coin in the market.

3. Average Hammer Price: The average hammer price for this coin is 255 euros, which can serve as a good indicator of the current market value.

4. Market Trends: Since the coin had a higher hammer price in the most recent auction, this suggests that interest in the coin may be increasing.

Taking these factors into account, an estimated maximum purchase price could be between the average hammer price (255 euros) and the most recent highest hammer price (310 euros). However, since the current condition is lower than previous ones, it is reasonable to adjust downwards.

Therefore, an estimated maximum purchase price could be around 280 euros. This reflects a balance between the increasing interest in the coin and its current condition.