Based on the provided data, we can observe that the coin in question had a starting price of 40 euros in the most recent auction, with an estimated price of 70 euros and an unspecified final value. The coin's condition is rated at 80 (MBC+).

Taking into account the previous prices of the coin in past auctions, as well as its current condition, we can estimate a maximum purchase price for this coin in the upcoming auction. Since the highest estimated price was 70 euros and considering that the condition is good but not excellent, we could consider a maximum purchase price around 65-75 euros.

Therefore, my estimate for the maximum purchase price for this coin in the next auction would be around 65-75 euros. It is important to note that this is just an estimate and the final price could vary depending on the demand at the auction.