This doesn't qualify as super, super cheap because you have to use a whole can of coconut milk and up to a whole jar of Thai curry paste. But it's good and easy.
Tofu in Thai Curry Sauce
1 can coconut milk
3 cloves garlic, sliced thin
From 2 T to one whole 4-oz jar Thai curry paste, either red or green
1/2 to 1 T brown sugar
2 lbs frozen (or not) mixed vegetables, such as stir-fry vegetables or California mix
1 14-oz package tofu, cubed
2 T soy sauce, or to taste
black pepper to taste
Put coconut milk in a pan with sliced garlic and bring to a boil. Add brown sugar and then 2 T curry paste, and keep adding more till it's as hot as you like. Then cook the vegetables in the coconut milk, or steam and then add to the pan. When the vegetables are nearly done, add the tofu and cook a few more minutes. Add soy sauce and black pepper. Serve over rice.