To estimate a maximum purchase price for the coin in question, we will consider several factors:

1. Starting Price: 35 euros, which is the initial price of the auction.
2. Current Condition: 30 (BC+), indicating a fairly low condition compared to the historical reference which has a condition of 70.
3. Previous Prices: In the 2019 auction, the coin with a condition of 70 sold for 80 euros, with a starting price of 75 euros and an estimated price of 125 euros.

Since the condition of the current coin is significantly lower (30 compared to 70), this will affect the final price.

The average hammer price of similar coins in the past is 62.5 euros, but since the condition is much lower, it is reasonable to adjust this price downward.

We can consider that, due to the low condition, the maximum purchase price could be in the range of 20 to 30 euros, as the condition drastically affects the value.

Therefore, an estimated maximum purchase price could be around 25 euros. This is a conservative value, taking into account the low condition and the price history.