Have you tried expedia

http://www.expedia.com

In a quick search I did in that ste I found tickets ranging from 1600 US$ up to 4000 US$ (costs will depend on the dates/season of travelling)

And no airline operates directly from doha, at least not to my knowledge. You will have to go through UAE, KSA, Bahrain, Singapore, Manila, and other countries; in the end is up to you.

Now a concern is how many stops are you willing to take: 1, 2 or more.

Depending on this you might get a nice selection on the airliners and the times.

Regards!!