Forget about buying books in this area.

What I do is order books through Amazon then have them shipped through the Aramex Shop&Ship service.

They provide you with a US mailbox (and UK mailbox if you want to order from Amazon UK) so the shipping charges from Amazon (or whatever the seller in the US is) are local shipping charges.

Aramex charge $8 for the first half kilo and $5.50 for each additional half kilo.
So for a kilo of books you are paying QAR 50 which is less than $14.
Check it out:

Aramex

There's a one-time non-recurring $35.00 subscription fee.

You can also try these 2 online sellers, one in Beirut and the other in London, for books of a more regional nature:

Saqi Books

AlDoukan