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

1. Current Condition: The coin has a condition of 75 (MBC), indicating that it is in fairly good shape, but not among the best qualities (FDC).

2. Auction History:
- The average hammer price for similar coins in the past is 84.28 euros.
- The coin has been auctioned 145 times, of which it has sold 128 times, indicating good demand.
- Previous hammer prices for coins with similar conditions (around 75) have varied, but some examples are:
- 70 euros (condition 70)
- 90 euros (condition 80)
- 130 euros (condition 85)

3. Starting Price and Average Starting Price:
- The starting price is 20 euros, and the average starting price is 55.23 euros. This suggests that the starting price is relatively low compared to the market value.

4. Recent Trends:
- In recent auctions, hammer prices for coins of similar condition have ranged from 60 to 130 euros.

Based on these factors, an estimated maximum purchase price for the coin could be in the range of 100 to 130 euros, considering that the condition is good and there is stable demand in the market.

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