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

1. Current Condition: The coin has a condition of 75 (MBC), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price for this coin in the past is 136.73 euros.
- The last auction with a known hammer price was 380 euros for a coin with a condition of 85, suggesting that the price can increase significantly with better condition.
- There are also previous auctions with hammer prices that vary, but are generally above the current starting price of 12 euros.

3. Price Trends:
- The average starting price has been 60.57 euros, indicating that buyers are willing to pay more than the starting price on many occasions.
- The coin has been sold in 13 out of 17 auctions, suggesting consistent demand.

4. Comparison with Previous Prices:
- In previous auctions, coins with similar conditions (75) have reached hammer prices of up to 35 euros (in 2022) and 20 euros (in 2018).

Taking all these factors into account, an estimated maximum purchase price for the coin with a condition of 75 could be in the range of 80 to 120 euros. This is based on the hammer price history and the current condition of the coin.

Therefore, a reasonable estimated maximum purchase price could be 100 euros.