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 75 (MBC), which indicates that it is in fairly good shape, but not the best possible condition.

2. Auction History:
- The average hammer price in previous auctions has been 144.23 euros.
- Hammer prices for coins with similar conditions (75) have varied, but there are examples where they have sold for 160 euros (in 2020) and 240 euros (in 2021).

3. Starting Price and Estimates:
- The current starting price is 90 euros, which is consistent with previous starting prices.
- The estimated price in past auctions has been up to 225 euros for similar conditions.

4. Sales Trends: Of the 17 times it has been auctioned, 14 have been sold, indicating good demand.

Based on this data, a reasonable maximum purchase price could be in the range of 160 to 180 euros, considering that the average hammer price is 144.23 euros and there are precedents for higher sales for similar conditions.

Therefore, an estimated maximum purchase price could be 180 euros.