Based on the provided data, here is an analysis to estimate a maximum purchase price for the coin in question:

1. Starting Price: 300 euros.
2. Condition: 70 (MBC-), which indicates a fairly good condition, although not the best possible.
3. Auction History: The coin has been auctioned once and sold on that occasion, suggesting there is interest in the coin at this price.

Since both the average hammer price and the average starting price are 300 euros, this indicates that the market has valued this coin within that range.

However, given that the condition is 70, you might consider that the price could be a bit lower if there are other influencing factors, such as current demand or the availability of similar coins in the market.

Estimated Maximum Purchase Price: You might consider a maximum purchase price of around 350 euros, which gives you a margin to compete in the auction, but also allows you not to exceed the value it has demonstrated in the past.

Remember that this is an estimate and the final price may vary depending on competition in the auction and other market factors.