Based on the provided data, we can observe that the coin in question has a grade of 80 (MBC+), indicating that it is in fairly good condition. Additionally, it has been auctioned in the past on several occasions, with varying starting and final prices.

The starting price for the upcoming auction is 30 euros, with a historical average starting price of 18 euros, and an average final price of 39 euros. Estimated prices in previous auctions have ranged between 20 and 30 euros.

Taking into account this data, as well as the coin's previous prices, we could estimate a maximum purchase price of around 35-40 euros. Considering the starting price of 30 euros and the average final price of 39 euros, an estimated maximum purchase price of 35-40 euros seems reasonable, given the coin's grade and historical prices.