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

1. Current Condition: The coin has a condition rating of 75 (MBC), indicating that it is in fairly good shape, although not the best possible condition.

2. Auction History:
- The average hammer price in previous auctions is 309.38 euros.
- In past auctions, hammer prices have varied, with a maximum of 400 euros and a minimum of 220 euros.
- The last auction with a known hammer price was 305 euros with a similar condition (80).

3. Starting Price and Estimates:
- The current starting price is 350 euros, which is higher than the average starting price of 246.43 euros.
- The estimated price of 350 euros also aligns with previous hammer prices, although it is slightly higher than the average.

4. Market Trends: Given that the coin has a history of successful sales and has not gone unsold, this suggests a steady demand.

Based on these factors, an estimated maximum purchase price could be in the range of 350 to 400 euros, considering that the starting price is 350 euros and that in the past, hammer prices of up to 400 euros have been reached for similar conditions.

Therefore, a reasonable maximum purchase price could be approximately 380 euros. This allows for some competition in the auction while also staying within the limits of what has been previously paid for coins of similar condition.