Where can I buy an inexpensive pair of Gi Pants with quilted knees?

I am trying to find a pair of Aikido pants with an elastic/drawstring waist combo. I have the traditional pants now, and I am constantly pulling them up and they don't stay on my hips, no matter how tight I tie them. I need a smaller size, but I am thinking the elastic waist would also help. But I don't want to spend a fortune!