All said and done you can buy 50,000 Choice Privileges points for $ 385 and exchange those for 32,500 United MileagePlus miles, and a finalcost of 1.18 cents permile.
The card even gives you an automatic 10 % rebate on all America Airlines awards (up to 100,000 AA miles redeemed per year), so the finalcost is 36,000 miles.