To estimate a maximum purchase price for the coin in question, we can analyze the provided data:

1. Starting price: 30 euros.
2. Coin condition: 75 (MBC), indicating good but not excellent condition.
3. Auction history:
- In 2015, the starting price was 20 euros, but no final price was recorded.
- In 2021, an estimated price of 58.77 euros was given, but it did not sell.
- In the same 2021 auction, the final price was 93.14 euros, indicating that despite the coin having a similar condition, market interest may have increased.

4. Average final price: 93.14 euros, which is an important figure as it reflects the value that buyers were willing to pay in the past.

Given that the coin has a condition of 75 and has had a final price of 93.14 euros in the past, it is reasonable to consider that interest in this coin could remain stable or even increase, especially if demand is high.

Estimation of the maximum purchase price:
- Considering the previous average final price (93.14 euros) and the fact that the starting price is 30 euros, a maximum purchase price could be set in a range between the average final price and 10-20% above it, given that the condition is good.

Therefore, an estimated maximum purchase price could be approximately 100-110 euros. This reflects both market interest and the condition of the coin.