I had mine done for 2 medium sized windows for around 600 HK$ (Of course the price depends on the fabric) at the following shop
Man Wah Curtain Co.
Shanghai Street No.626, G/F, Mong Kok
Tel. 23929767, 27873679, Fax 2390800.
I have a habit of scanning namecards, but this one is Chinese only. If you still want it, PM me your email address.
It is not as cheap as China, but 70 for the KCR and 150 for the visa at the border (If you have HKID) needs to be accounted. and you would most probably need to go twice