To estimate a maximum purchase price for the coin that will be auctioned, we will consider several factors:

1. Condition of the coin: The coin in question has a condition of 100 (MS), indicating that it is in excellent condition. This generally translates to a higher value compared to coins with lower conditions.

2. Starting price: The starting price is 1500 euros. This is the starting point for the auction.

3. Price history: By observing previous auction prices of similar coins, we can see that the average hammer price is 224.45 euros, but there are examples of much higher hammer prices, such as 1200 euros in a previous auction.

4. Auction trends: The coin has been auctioned 54 times, of which 52 have sold. This indicates high demand and consistent interest in this coin.

5. Previous hammer prices: Previous hammer prices for coins with similar conditions (85-95) have reached up to 1200 euros. Given that the condition of the coin in question is superior, it is reasonable to expect that the hammer price will be higher.

Taking all these factors into account, an estimated maximum purchase price could be in the range of 1500 to 2000 euros, considering that the condition is excellent and there is a price history that supports this estimate. However, since the starting price is 1500 euros, it is likely that the hammer price will not significantly exceed this value unless there is intense competition in the auction.

Therefore, a reasonable maximum purchase price could be 1800 euros.