I've been looking for a laptop backpack with reasonable price and I found it at Tesco, Bandar Utama. The normal price is RM75 but I've got it even cheaper, with 20% discount (RM63.20). The most important thing for me is my 15.4" laptop fits well into the backpack.
I don't think you can get a better bargain than this. The quality is not bad. However, if you are looking for something like the Targus brand, be ready to fork out RM150-300. Even the best deal I could get on ebay was RM85 for a second hand backpack, excluding the delivery charges of RM20.
So, if you are looking for one, I've already grabbed the last blue coloured model.