I generally don’t find purchasing miles to be lucrative. US Airways used to have a pretty good price, but they’ve raised prices since then to make it not quite such a good value.
At the bottom of the range the price is not great. If you buy 6,000 miles, the price comes out to 2.76 cents per point, which kinda sucks. At exactly 36,000 points, the price drops down to 2.37 cents which isn’t horrible.
They’ve offered miles for less earlier this year, so I don’t consider this a great deal, but it is a shade better right at 36,000 miles than it has been in the past.