Huong Sen is either the cheapest or one of the least expensive places to get good quality vegetarian/vegan food.
A small place set up deli counter-style. The plain fried tofu is delicious and a real bargain--many tofu-based dishes on the menu. They could use a few more vegetable dishes.
Worth at least two visits to get a sampling of dishes. Located in a small shopping center that is about 90% Vietnamese businesses.
You will spend about half as much as you would in most veggie restaurants. Cook your own rice at home and buy your entrees, appetizers here.
Cons: tight parking when shopping center busy, language barrier, menu somewhat confusing on first visit