Based on the provided data, we can observe that the coin in question has had varying starting and final prices in previous auctions. The current starting price is 18 euros, with a historical average starting price of 21.15 euros and a historical average final price of 45.83 euros.

The conservation grade of the coin is described as 70 (MBC-), indicating a medium to low conservation level.

Taking into account the coin's previous auction prices and its current conservation state, we can estimate a maximum purchase price. Given the current starting price of 18 euros and the historical average final price of 45.83 euros, we could consider an estimated maximum purchase price around 40-50 euros, considering the medium to low conservation level of the coin.

It's important to note that the final auction price may vary depending on the demand at that specific moment, so it's advisable to monitor the auction's progress to adjust the offer accordingly.