To estimate a maximum purchase price for the coin in question, we can consider several factors based on the provided data:

1. Current Condition: The coin has a condition rating of 80 (MBC+), indicating that it is in relatively good shape. This suggests that its value should be in the upper range of previous auction prices.

2. Previous Auction Prices: Looking at previous auction prices, we can see that they have varied considerably. For example, in 2014 it sold for 200 euros, and in 2020 for 170 euros. However, there are also lower auction prices, such as 32 euros in 2012.

3. Average Auction Price: The average auction price for this coin is 99.56 euros, which can serve as a good reference point.

4. Current Starting Price: The starting price is 35 euros, which is quite low compared to previous auction prices.

5. Sales Trends: The coin has been auctioned 28 times, of which it has sold 12 times. This indicates a moderate interest in the coin, which may influence its price.

Given all this, an estimated maximum purchase price could be in the range of 120 to 150 euros, considering that the condition is good and that previous auction prices have reached higher figures. However, since the starting price is 35 euros, the competition in the auction may not be very intense, which could result in a lower final price.

Therefore, a reasonable maximum purchase price could be 120 euros.