When the price of Brooke Astor’s sprawling Park Avenue duplex dropped from $46 million to $24.9 million, we told you that you couldn’t afford not to buy it. But that was before Astor’s son, Anthony Marshall, and his wife Charlene’s legal fees ballooned to more than $7 million as he appeals his conviction on the charge of swindling his mother out of $60 million. Now, the Upper East Side building’s co-op board is considering a bid “in the high teens” for the five-bedroom, six-terrace duplex with views of Park Avenue and Central Park. While the Astor estate, which has yet to determine Anthony’s share, hopes for a higher bid, the fact that her son and his wife accepted such a low offer is a sign that they “are desperate for money,” a local broker told the Post. Sorry about that — we always forget to factor legacy-destroying crooks into our real-estate calculations. But if you can scrounge up $20 million, looks like the fifteenth and sixteenth floors are yours.