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

1. Current Condition: The coin has a condition of 70 (MS-). This is an important factor, as coins in better condition tend to reach higher prices.

2. Auction History:
- The average hammer price in previous auctions is 2037.15 euros.
- In past auctions, the coin has reached hammer prices that varied, but generally, the hammer prices have been in the range of 2000 to 3000 euros, depending on the condition and other factors.

3. Starting Price and Estimates:
- The current starting price is 1500 euros, which is a reasonable starting point.
- The estimated price for this auction is 2500 euros, indicating expectations that the coin will sell for a higher price.

4. Sales Trends:
- The coin has been sold in 21 out of 23 auctions, indicating good demand and a history of successful sales.

5. Comparison with Previous Prices:
- In previous auctions, coins with similar conditions have reached hammer prices of up to 3000 euros.

Based on these factors, an estimated maximum purchase price could be in the range of 2500 to 2800 euros, considering that condition is a key factor and that the average hammer price has been 2037.15 euros.

Therefore, a reasonable maximum purchase price could be 2800 euros.