Theory. I love their dress pants. They're expensive but I love that you can find really great deals on staple Theory pieces at Nordstrom Rack and TJ Maxx. I've accumulated a whole suit (black skirt, pants, and blazer) for under $200. Of course, finding those pieces in your size for at such a good price is hard, but it can be done!
I lately source some stuff in a dropship store with product range for sportwear to women fashion stuff. They might have got vest and pant. But not sure if it is supplied in suits. Hope you can find what you want.