This is a different event to the normal ones that are free.

You can ring the Khalifa Tennis Complex to enquire about tickets - 4409666

Prices are QR10 for upper tiers, QR20 for middle tiers and QR50-QR150 for lower tiers.

I got all this info from a simple google search, which led me to this page; http://www.sonyericsson-championships.com/en/tickets/