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 75 (MBC), indicating that it is in relatively good shape, but not of the highest quality (FDC).

2. Current Starting Price and Previous Prices: The current starting price is 170 euros. In previous auctions, the average hammer price has been 247.38 euros, suggesting that there is potential for a sale price higher than the starting price.

3. Sales History: The coin has been auctioned 47 times, of which it has sold 45 times. This indicates high demand and a good sales record.

4. Previous Hammer Prices: Looking at previous hammer prices for coins with similar conditions (70-80), we can see that they have reached hammer prices of up to 240 euros in the past.

5. Recent Trends: In the most recent auctions, hammer prices have varied, but there are examples of sales that have exceeded 200 euros, even with similar conditions.

Based on these factors, an estimated maximum purchase price could be in the range of 240 to 280 euros, considering that the average hammer price is 247.38 euros and that there are examples of previous sales that have reached higher prices.

Therefore, a reasonable maximum purchase price could be 250 euros.