American Airlines has had almost monthly promotions for buying miles. Thing to remember is that you can only buy or be gifted maximum of 40K American Airlines AAdvantage miles on a calendar year.
The current offer is for maximum of 10K bonus miles for buying 36K to 40K AAdvantage miles. If you buy the minimum required to get the maximum bonus, the price of a mile under this offer is 2.4 cents each.
This is not the best offer for buying American Airlines AAdvantage miles that have been out there lately. If you do, however, need a number of miles to make that international business/first class trip to happen, it can make sense.