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

1. Current Condition: The coin has a condition rating of 90 (EBC), indicating that it is in good shape. This is a positive factor that can increase its value.

2. Previous Auction Prices:
- In 2019, the coin was auctioned with a starting price of 1500 and a final price of 1600 with a condition of 95.
- In 2019, it was also auctioned with a starting price of 925 and a final price of 1188 with a condition of 80.
- In 2014, it was auctioned with a starting price of 1800 and an estimated price of 2500, although the final price is unknown.
- In 2014, it was also auctioned with a starting price of 1200 and a final price of 1200, but with no information on the condition.

3. Average Starting and Final Prices: The average starting price is 1237.5 and the average final price is 1249.8. This suggests that, in general, coins of this reference tend to sell close to these values.

4. Sales Trends: The coin has sold in 5 out of the 6 times it has been auctioned, indicating good demand.

5. Current Starting Price: The current starting price is 1200, which is slightly lower than the average starting price.

Based on these factors, especially considering the condition of 90 and previous final prices, an estimated maximum purchase price could be in the range of 1400 to 1600 euros. This is because, although the starting price is 1200, the condition and previous final prices suggest it could reach a higher value at auction.

Therefore, a reasonable estimated maximum purchase price could be 1500 euros.