To estimate a maximum purchase price for the coin in question, we can analyze the provided data, especially the previous auction prices and the conditions of the auctioned coins.

1. General Data:
- Current starting price: €250
- Average starting price: €318.34
- Average hammer price: €443.6
- Times auctioned in the past: 55
- Times sold in the past: 52

2. Analysis of Previous Prices:
- Previous hammer prices for coins in similar conditions (95, 90, 85) have ranged between €220 and €730.
- Most hammer prices for conditions of 90 and 95 have been above €400.

3. Estimation:
- Since there is no information about the condition of the current coin, it is prudent to consider a price range based on the highest conditions that have sold in the past.
- The highest recorded hammer price was €730 for a condition of 95, and the lowest was €220 for a condition of 70.

4. Conclusion:
- Considering the average hammer price (€443.6) and previous hammer prices, an estimated maximum purchase price could be between €400 and €600, depending on demand and collector interest at the auction.

Therefore, a reasonable estimated maximum purchase price for this coin could be approximately €600.